#include <bits/stdc++.h>
#include <random>
using namespace std;
const int N = 2e5+10;
typedef long long ll;
int n,m,k;
string s[N];
ll cnt[N][5],val[N];
mt19937 rnd(time(0));
int main(){
   ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
   cin >> n >> m >> k;
   ll sum = 0;
   for(int i = 1; i <= n ; ++ i){
    cin >> s[i];
    val[i] = rnd();
    for(int j = 0; j < m; ++ j) cnt[j][s[i][j]-'A']+=val[i];
    sum += val[i];
   }
   for(int i = 1; i <= n ; ++ i){
    ll cur = sum * m;
    for(int j = 0; j < m ; ++ j)cur -= cnt[j][s[i][j]-'A'];
    if(cur == (sum-val[i]) * k){
      cout << i << "\n";
      return 0;
    }
   }
   return 0;
}