#include <bits/stdc++.h>

using namespace std;

const int N = 1e5 + 5;

int n, m, k, cnt[N][4];
string s[N];

void solve(){
    cin >> n >> m >> k;
    for (int i = 1; i <= n; ++ i){
        cin >> s[i];
        for (int j = 0; j < m; ++ j) cnt[j][s[i][j] - 'A'] ++;
    }

    for (int i = 1; i <= n; ++ i){
        long long dist = 0;
        for (int j = 0; j < m; ++ j) dist += (n - cnt[j][s[i][j] - 'A']);
        if (dist == 1ll * k * (n - 1)){
            cout << i;
            return;
        }
    }
}

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    solve();

    return 0;
}