#include <bits/stdc++.h>
#define int long long
#define ii pair<int, int>
#define iii pair<int,ii>
#define vii vector<ii>
#define fi first
#define se second
#define endl '\n'
#define show(T) {for (auto x:T) cout<<x<<' ';cout<<endl;}
#define all(T) T.begin(),T.end()
using namespace std;
const double eps = 0.0001;
const int mod =/*998244353*/ 1e9+7;
const int N = 1005;
const int MATRIX_SIZE = 64;
const int BLOCK=500;
const long long oo=1e18;
int n,m,k,num[100005][6];
vector <vector<char>> T;
char c;
mt19937 rd(chrono::steady_clock::now().time_since_epoch().count());
int Rand(int l,int r){
    return uniform_int_distribution<int>(l,r)(rd);
}
int get(int a,int b){
    int res=0;
    for (int i=1;i<=m;++i)
        res+=(T[a][i]!=T[b][i]);
    return res;
}
bool check(int pos){
    for (int i=1,trol;i<=30;++i){
        do{
            trol=Rand(1,n);
        } while (trol==pos);
        if (get(trol,pos)!=k) return false;
    }
    return true;
}
void solve(){
    cin>>n>>m>>k;
    T.resize(n+5,vector<char>(m+5));
    for (int i=1;i<=n;++i){
        for (int j=1;j<=m;++j){
            // cout<<i<<' '<<j<<endl;
            cin>>c;
            ++num[j][c-'A'];
            T[i][j]=c;
        }
    }
    for (int i=1;i<=n;++i){
        int sum=0;
        for (int j=1;j<=m;++j)
            sum+=num[j][T[i][j]-'A']-1;
        // cout<<i<<' '<<sum<<endl;
        if (sum!=(m-k)*(n-1)) continue;
        if (check(i)) return void(cout<<i);
    }
}
main() {
    //freopen("ok.inp","r",stdin);
   //freopen("kiemtra.out","w",stdout);
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    solve();
    // cout<<endl<<clock()/1000.0;
}