#include <bits/stdc++.h>
#define int long long
#define lb lower_bound
#define ub upper_bound
#define fi first
#define se second
#define pb emplace_back
#define For(i, x, y) for (int i = (x); i <= (y); i ++)
#define rep(i, x, y) for (int i = (x); i >= (y); i --)
#define pii pair<int, int>
#define all(v) v.begin(), v.end()
#define sz(v) (int)((v).size())
#define ull unsigned long long
#define ls (p << 1)
#define rs (p << 1 | 1)
#define mp make_pair
#define i128 __int128
#define db long double
#define vi vector< int >
#define mem(v, x) memset(v, x, sizeof(v))
#define A3 array< int, 3 >
#define A4 array< int, 4 >
#define vpii vector< pair< int, int > >
using namespace std;
mt19937_64 rnd(time(0));
template< typename T > void cmin(T &x, T y) { return x = min(x, y), void(); }
template< typename T > void cmax(T &x, T y) { return x = max(x, y), void(); }
int ksm(int x, int y, int p) {
    int v = 1; x %= p;
    while (y) v = 1ll * v * ((y & 1) ? x : 1) % p, x = 1ll * x * x % p, y >>= 1;
    return (v % p + p) % p;
}
bool MemoryST;
const int N = 1e5 + 5;
const int mod = 998244353;
const long long INF = 1e18;
const int base = 13131;
int n, m, k;
string s[N];
ull val[N], f[N][4];
void solve() {
	cin >> n >> m >> k;
	For (i, 1, n) val[i] = rnd();
	For (i, 1, n) {
		cin >> s[i]; s[i] = " " + s[i];
		For (j, 1, m) f[j][s[i][j] - 'A'] += val[i];
	}
	ull res = 0;
	For (i, 1, n) res += (m - k) * val[i];
	For (i, 1, n) {
		ull sum = 0;
		For (j, 1, m) sum += f[j][s[i][j] - 'A'];
		sum -= m * val[i];
		if (sum == res - (m - k) * val[i]) return cout << i, void(); 
	}
    return;
}
bool MemoryED;
signed main() {
    ios :: sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    cerr << fixed << setprecision(6) << (&MemoryST - &MemoryED) / 1048576.0 << "MB\n";
    int TESTCNT = 1;
    // cin >> TESTCNT;
    while (TESTCNT --) solve();
    cerr << endl << 1e3 * clock() / CLOCKS_PER_SEC << "ms"; 
    return 0;
}