#include <bits/stdc++.h>
using namespace std;
using ull = unsigned long long;
mt19937_64 rnd(20060130);
constexpr int N = 1e5 + 5;
int n, m, k;
string str[N];
ull s, f[N], buc[N][4];
int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  #ifdef ALEX_WEI
    FILE* IN = freopen("1.in", "r", stdin);
    FILE* OUT = freopen("1.out", "w", stdout);
  #endif
  cin >> n >> m >> k;
  for(int i = 1; i <= n; i++) cin >> str[i];
  for(int i = 1; i <= n; i++) {
    s += f[i] = rnd();
    for(int j = 0; j < m; j++) {
      int c = str[i][j] - 'A';
      for(int d = 0; d < 4; d++) if(c != d) buc[j][d] += f[i];
    }
  }
  for(int i = 1; i <= n; i++) {
    ull sum = 0;
    for(int j = 0; j < m; j++) sum += buc[j][str[i][j] - 'A'];
    if(sum == (s - f[i]) * k) cout << i << "\n", exit(0);
  }
  cerr << 1e3 * clock() / CLOCKS_PER_SEC << " ms\n";
  return 0;
}
/*
g++ F.cpp -o F -std=c++14 -O2 -DALEX_WEI
*/