#line 1 "A.cpp"
// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
#include<bits/stdc++.h>
using namespace std;

using ll = long long;
using ull = unsigned long long;
template <class T>
using pq = priority_queue<T>;
template <class T>
using qp = priority_queue<T, vector<T>, greater<T>>;
#define vec(T, A, ...) vector<T> A(__VA_ARGS__);
#define vvec(T, A, h, ...) vector<vector<T>> A(h, vector<T>(__VA_ARGS__));
#define vvvec(T, A, h1, h2, ...) vector<vector<vector<T>>> A(h1, vector<vector<T>>(h2, vector<T>(__VA_ARGS__)));

#ifndef RIN__LOCAL
#define endl "\n"
#endif
#define spa ' '
#define len(A) A.size()
#define all(A) begin(A), end(A)

#define fori1(a) for(ll _ = 0; _ < (a); _++)
#define fori2(i, a) for(ll i = 0; i < (a); i++)
#define fori3(i, a, b) for(ll i = (a); i < (b); i++)
#define fori4(i, a, b, c) for(ll i = (a); ((c) > 0 || i > (b)) && ((c) < 0 || i < (b)); i += (c))
#define overload4(a, b, c, d, e, ...) e
#define fori(...) overload4(__VA_ARGS__, fori4, fori3, fori2, fori1)(__VA_ARGS__)

template <typename T>
vector<tuple<ll, T>> ENUMERATE(vector<T> &A, ll s = 0){
    vector<tuple<ll, T>> ret(A.size());
    for(int i = 0; i < A.size(); i++) ret[i] = {i + s, A[i]};
    return ret;
}

vector<tuple<ll, char>> ENUMERATE(string &A, ll s = 0){
    vector<tuple<ll, char>> ret(A.size());
    for(int i = 0; i < A.size(); i++) ret[i] = {i + s, A[i]};
    return ret;
}

#define enum1(A) fori(A.size())
#define enum2(a, A) for(auto a:A)
#define enum3(i, a, A) for(auto&& [i, a]: ENUMERATE(A))
#define enum4(i, a, A, s) for(auto&& [i, a]: ENUMERATE(A, s))
#define enum(...) overload4(__VA_ARGS__, enum4, enum3, enum2, enum1)(__VA_ARGS__)

template <typename T, typename S>
vector<tuple<T, S>> ZIP(vector<T> &A, vector<S> &B){
    int n = min(A.size(), B.size());
    vector<tuple<T, S>> ret(n);
    for(int i = 0; i < n; i++) ret[i] = {A[i], B[i]};
    return ret;
}

template <typename T, typename S>
vector<tuple<ll, T, S>> ENUMZIP(vector<T> &A, vector<S> &B, ll s = 0){
    int n = min(A.size(), B.size());
    vector<tuple<ll, T, S>> ret(n);
    for(int i = 0; i < n; i++) ret[i] = {i + s, A[i], B[i]};
    return ret;
}

#define zip4(a, b, A, B) for(auto&& [a, b]: ZIP(A, B))
#define enumzip5(i, a, b, A, B) for(auto&& [i, a, b]: ENUMZIP(A, B))
#define enumzip6(i, a, b, A, B, s) for(auto&& [i, a, b]: ENUMZIP(A, B, s))
#define overload6(a, b, c, d, e, f, g, ...) g
#define zip(...) overload6(__VA_ARGS__, enumzip6, enumzip5, zip4, _, _, _)(__VA_ARGS__)

vector<char> stoc(string &S){
    int n = S.size();
    vector<char> ret(n);
    for(int i = 0; i < n; i++) ret[i] = S[i];
    return ret;
}

#define INT(...) int __VA_ARGS__; inp(__VA_ARGS__);
#define LL(...) ll __VA_ARGS__; inp(__VA_ARGS__);
#define STRING(...) string __VA_ARGS__; inp(__VA_ARGS__);
#define CHAR(...) char __VA_ARGS__; inp(__VA_ARGS__);
#define VEC(T, A, n) vector<T> A(n); inp(A);
#define VVEC(T, A, n, m) vector<vector<T>> A(n, vector<T>(m)); inp(A);

const ll MOD1 = 1000000007;
const ll MOD9 = 998244353;

template<class T> auto min(const T& a){
    return *min_element(all(a));
}
template<class T> auto max(const T& a){
    return *max_element(all(a));
}
template <class T, class S>
auto clamp(T &a, const S &l, const S &r) {
    return (a > r ? r : a < l ? l : a);
}
template <class T, class S>
inline bool chmax(T &a, const S &b) {
    return (a < b ? a = b, 1 : 0);
}
template <class T, class S>
inline bool chmin(T &a, const S &b) {
    return (a > b ? a = b, 1 : 0);
}
template <class T, class S>
inline bool chclamp(T &a, const S &l, const S &r) {
    auto b = clamp(a, l, r);
    return (a != b ? a = b, 1 : 0);
}

void FLUSH(){cout << flush;}
void print(){cout << endl;}
template <class Head, class... Tail>
void print(Head &&head, Tail &&... tail) {
    cout << head;
    if (sizeof...(Tail)) cout << spa;
    print(forward<Tail>(tail)...);
}
template<typename T>
void print(vector<T> &A){
    int n = A.size();
    for(int i = 0; i < n; i++){
        cout << A[i];
        if(i != n - 1) cout << ' ';
    }
    cout << endl;
}
template<typename T>
void print(vector<vector<T>> &A){
    for(auto &row: A) print(row);
}
template<typename T, typename S>
void print(pair<T, S> &A){
    cout << A.first << spa << A.second << endl;
}
template<typename T, typename S>
void print(vector<pair<T, S>> &A){
    for(auto &row: A) print(row);
}
template<typename T, typename S>
void prisep(vector<T> &A, S sep){
    int n = A.size();
    for(int i = 0; i < n; i++){
        cout << A[i];
        if(i == n - 1) cout << endl;
        else cout << sep;
    }
}
template<typename T, typename S>
void priend(T A, S end){
    cout << A << end;
}
template<typename T>
void priend(T A){
    priend(A, spa);
}
template<class... T>
void inp(T&... a){
    (cin >> ... >> a);
}
template<typename T>
void inp(vector<T> &A){
    for(auto &a:A) cin >> a;
}
template<typename T>
void inp(vector<vector<T>> &A){
    for(auto &row:A) inp(row);
}
template<typename T, typename S>
void inp(pair<T, S> &A){
    inp(A.first, A.second);
}
template<typename T, typename S>
void inp(vector<pair<T, S>> &A){
    for(auto &row: A) inp(row.first, row.second);
}

template<typename T>
T sum(vector<T> &A){
    T tot = 0;
    for(auto a:A) tot += a;
    return tot;
}

template<typename T>
pair<vector<T>, map<T, int>> compression(vector<T> X){
    sort(all(X));
    X.erase(unique(all(X)), X.end());
    map<T, int> mp;
    for(int i = 0; i < X.size(); i++) mp[X[i]] = i;
    return {X, mp};
}

vector<vector<int>> read_edges(int n, int m, bool direct=false, int indexed=1){
    vector<vector<int>> edges(n, vector<int>());
    for(int i = 0; i < m; i++){
        INT(u, v);
        u -= indexed;
        v -= indexed;
        edges[u].push_back(v);
        if(!direct) edges[v].push_back(u);
    }
    return edges;
}

vector<vector<int>> read_tree(int n, int indexed=1){
    return read_edges(n, n - 1, false, indexed);
}

template<typename T>
vector<vector<pair<int, T>>> read_wedges(int n, int m, bool direct=false, int indexed=1){
    vector<vector<pair<int, T>>> edges(n, vector<pair<int, T>>());
    for(int i = 0; i < m; i++){
        INT(u, v);
        T w;
        inp(w);
        u -= indexed;
        v -= indexed;
        edges[u].push_back({v, w});
        if(!direct) edges[v].push_back({u, w});
    }
    return edges;
}

template<typename T>
vector<vector<pair<int, T>>> read_wtree(int n, int indexed=1){
    return read_wedges<T>(n, n - 1, false, indexed);
}

#line 2 "Library/C++/other/Modint.hpp"

template<int MOD>
struct Modint{
    int x;
    Modint() : x(0){}
    Modint(int64_t y){
        if(y >= 0) x = y % MOD;
        else x = (y % MOD + MOD) % MOD;
    }

    Modint &operator+=(const Modint &p){
        x += p.x;
        if(x >= MOD) x -= MOD;
        return *this;
    }

    Modint &operator-=(const Modint &p){
        x -= p.x;
        if(x < 0) x += MOD;
        return *this;
    }

    Modint &operator*=(const Modint &p){
        x = int(1LL * x * p.x % MOD);
        return *this;
    }

    Modint &operator/=(const Modint &p){
        *this *= p.inverse();
        return *this;
    }

    Modint &operator%=(const Modint &p){
        assert(p.x == 0);
        return *this;
    }

    Modint operator-() const{
        return Modint(-x);
    }

    Modint& operator++() {
        x++;
        if (x == MOD) x = 0;
        return *this;
    }

    Modint& operator--() {
        if (x == 0) x = MOD;
        x--;
        return *this;
    }

    Modint operator++(int) {
        Modint result = *this;
        ++*this;
        return result;
    }

    Modint operator--(int) {
        Modint result = *this;
        --*this;
        return result;
    }

    friend Modint operator+(const Modint &lhs, const Modint &rhs){
        return Modint(lhs) += rhs;
    }

    friend Modint operator-(const Modint &lhs, const Modint &rhs){
        return Modint(lhs) -= rhs;
    }

    friend Modint operator*(const Modint &lhs, const Modint &rhs){
        return Modint(lhs) *= rhs;
    }

    friend Modint operator/(const Modint &lhs, const Modint &rhs){
        return Modint(lhs) /= rhs;
    }

    friend Modint operator%(const Modint &lhs, const Modint &rhs){
        assert(rhs.x == 0);
        return Modint(lhs);
    }

    bool operator==(const Modint &p) const{
        return x == p.x;
    }

    bool operator!=(const Modint &p) const{
        return x != p.x;
    }

    bool operator<(const Modint &rhs) const{
        return x < rhs.x;
    }

    bool operator<=(const Modint &rhs) const{
        return x <= rhs.x;
    }

    bool operator>(const Modint &rhs) const{
        return x > rhs.x;
    }

    bool operator>=(const Modint &rhs) const{
        return x >= rhs.x;
    }

    Modint inverse() const{
        int a = x, b = MOD, u = 1, v = 0, t;
        while(b > 0){
            t = a / b;
            a -= t * b;
            u -= t * v;
            swap(a, b);
            swap(u, v);
        }
        return Modint(u);
    }

    Modint pow(int64_t k) const{
        Modint ret(1);
        Modint y(x);
        while(k > 0){
            if(k & 1) ret *= y;
            y *= y;
            k >>= 1;
        }
        return ret;
    }

    friend ostream &operator<<(ostream &os, const Modint &p){
        return os << p.x;
    }

    friend istream &operator>>(istream &is, Modint &p){
        int64_t y;
        is >> y;
        p = Modint<MOD>(y);
        return (is);
    }

    static int get_mod(){
        return MOD;
    }
};

struct Arbitrary_Modint{
    int x;
    static int MOD;

    static void set_mod(int mod){
        MOD = mod;
    }

    Arbitrary_Modint() : x(0){}
    Arbitrary_Modint(int64_t y){
        if(y >= 0) x = y % MOD;
        else x = (y % MOD + MOD) % MOD;
    }

    Arbitrary_Modint &operator+=(const Arbitrary_Modint &p){
        x += p.x;
        if(x >= MOD) x -= MOD;
        return *this;
    }

    Arbitrary_Modint &operator-=(const Arbitrary_Modint &p){
        x -= p.x;
        if(x < 0) x += MOD;
        return *this;
    }

    Arbitrary_Modint &operator*=(const Arbitrary_Modint &p){
        x = int(1LL * x * p.x % MOD);
        return *this;
    }

    Arbitrary_Modint &operator/=(const Arbitrary_Modint &p){
        *this *= p.inverse();
        return *this;
    }

    Arbitrary_Modint &operator%=(const Arbitrary_Modint &p){
        assert(p.x == 0);
        return *this;
    }

    Arbitrary_Modint operator-() const{
        return Arbitrary_Modint(-x);
    }

    Arbitrary_Modint& operator++() {
        x++;
        if (x == MOD) x = 0;
        return *this;
    }

    Arbitrary_Modint& operator--() {
        if (x == 0) x = MOD;
        x--;
        return *this;
    }

    Arbitrary_Modint operator++(int) {
        Arbitrary_Modint result = *this;
        ++*this;
        return result;
    }

    Arbitrary_Modint operator--(int) {
        Arbitrary_Modint result = *this;
        --*this;
        return result;
    }

    friend Arbitrary_Modint operator+(const Arbitrary_Modint &lhs, const Arbitrary_Modint &rhs){
        return Arbitrary_Modint(lhs) += rhs;
    }

    friend Arbitrary_Modint operator-(const Arbitrary_Modint &lhs, const Arbitrary_Modint &rhs){
        return Arbitrary_Modint(lhs) -= rhs;
    }

    friend Arbitrary_Modint operator*(const Arbitrary_Modint &lhs, const Arbitrary_Modint &rhs){
        return Arbitrary_Modint(lhs) *= rhs;
    }

    friend Arbitrary_Modint operator/(const Arbitrary_Modint &lhs, const Arbitrary_Modint &rhs){
        return Arbitrary_Modint(lhs) /= rhs;
    }

    friend Arbitrary_Modint operator%(const Arbitrary_Modint &lhs, const Arbitrary_Modint &rhs){
        assert(rhs.x == 0);
        return Arbitrary_Modint(lhs);
    }

    bool operator==(const Arbitrary_Modint &p) const{
        return x == p.x;
    }

    bool operator!=(const Arbitrary_Modint &p) const{
        return x != p.x;
    }

    bool operator<(const Arbitrary_Modint &rhs) {
        return x < rhs.x;
    }

    bool operator<=(const Arbitrary_Modint &rhs) {
        return x <= rhs.x;
    }

    bool operator>(const Arbitrary_Modint &rhs) {
        return x > rhs.x;
    }

    bool operator>=(const Arbitrary_Modint &rhs) {
        return x >= rhs.x;
    }

    Arbitrary_Modint inverse() const{
        int a = x, b = MOD, u = 1, v = 0, t;
        while(b > 0){
            t = a / b;
            a -= t * b;
            u -= t * v;
            swap(a, b);
            swap(u, v);
        }
        return Arbitrary_Modint(u);
    }

    Arbitrary_Modint pow(int64_t k) const{
        Arbitrary_Modint ret(1);
        Arbitrary_Modint y(x);
        while(k > 0){
            if(k & 1) ret *= y;
            y *= y;
            k >>= 1;
        }
        return ret;
    }

    friend ostream &operator<<(ostream &os, const Arbitrary_Modint &p){
        return os << p.x;
    }

    friend istream &operator>>(istream &is, Arbitrary_Modint &p){
        int64_t y;
        is >> y;
        p = Arbitrary_Modint(y);
        return (is);
    }

    static int get_mod(){
        return MOD;
    }
};
int Arbitrary_Modint::MOD = 998244353;

using modint9 = Modint<998244353>;
using modint1 = Modint<1000000007>;
using modint = Arbitrary_Modint;
#line 2 "Library/C++/other/RandomNumberGenerator.hpp"

struct RandomNumberGenerator{
    mt19937 mt;
    RandomNumberGenerator() : mt(chrono::steady_clock::now().time_since_epoch().count()) {}

    int operator()(int a, int b){
        uniform_int_distribution< int > dist(a, b - 1);
        return dist(mt);
    }

    int operator()(int b){
        return (*this)(0, b);
    }
};
#line 234 "A.cpp"
using mint = Arbitrary_Modint;

void solve(){
    INT(n, m, k);
    k = m - k;
    VEC(string, S, n);
    RandomNumberGenerator rnd;
    vec(bool, cand, n, true);

    while(1){
        mint::set_mod(rnd(1 << 29, 1 << 30));
        vec(mint, X, n);
        fori(i, n) X[i] = rnd(1 << 29, 1 << 30);
        vvec(mint, tot, m, 4, 0);
        mint h = 0;
        fori(i, n){
            h += X[i];
            fori(j, m) tot[j][S[i][j] - 'A'] += X[i];
        }
        h *= k;

        int cnt = 0;
        fori(i, n){
            mint hh = 0;
            fori(j, m){
                hh += tot[j][S[i][j] - 'A'];
            }
            hh -= X[i] * (m - k);
            if(h != hh){
                cand[i] = false;
            }
            if(cand[i]) cnt++;
        }
        if(cnt == 1) break;
        assert(cnt >= 2);
    }
    fori(i, n){
        if(cand[i]){
            print(i + 1);
            break;
        }
    }
}

int main(){
    cin.tie(0)->sync_with_stdio(0);
    // cout << fixed << setprecision(12);
    int t;
    t = 1;
    // cin >> t;
    while(t--) solve();
    return 0;
}