#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

ll MOD = 1e13 + 7;

int main() {
    ll n,m,k; cin >> n >> m >> k;

    vector<ll> v(n); 
    default_random_engine rng;
    
    for(int i = 0; i < n; i++) {    
        v[i] = uniform_int_distribution<ll>(1e10, 1e13)(rng);
    }
    vector<string> S(n);
    vector<vector<ll>> cnt(m, vector<ll>(4));
    for(int i = 0; i < n; i++) {
        cin >> S[i];
        for(int j = 0; j < m; j++) {
            cnt[j][S[i][j] - 'A'] += v[i];
            cnt[j][S[i][j] - 'A'] %= MOD;
        }
    }

    ll allsum = 0;
    for(int i = 0; i < n; i++) {
        allsum = (allsum + v[i]) % MOD;
    }

    for(int i = 0; i < n; i++) {
        ll tot = 0;
        for(int j = 0; j < m; j++) {
            for(int k = 0; k < 4; k++) {
                if(k == S[i][j] - 'A') continue;
                tot = (tot + cnt[j][k]) % MOD;
            }
        }
        ll allbut = (allsum - v[i] + MOD) % MOD;
        ll target = (allbut * k) % MOD;
        if(tot == target) {
            cout << i + 1 << endl;
            return 0;
        }
    }




}