// Editorial OP!
#include <bits/stdc++.h>
using namespace std;
const int N = 4105;
int n, m, k, sum[N], val[N], f[4][N];
char a[N][N];
int toint (char c) {
if (c == 'A') return 0;
if (c == 'C') return 1;
if (c == 'G') return 2;
return 3;
}
int main(){
mt19937 rd(chrono::steady_clock::now().time_since_epoch().count());
cin >> n >> m >> k;
for (int i = 1; i <= n; i++) cin >> a[i];
for (int i = 1; i <= n; i++) val[i] = rd() % 100000 + 1;
for (int i = 0; i < m; i++) for (int j = 1; j <= n; j++) f[toint(a[j][i])][i] += val[j];
for (int i = 1; i <= n; i++) {
for (int j = 0; j < m; j++) for (int k = 0; k < 4; k++) if (k != toint(a[i][j])) sum[i] += f[k][j];
int cur = 0;
for (int j = 1; j <= n; j++) if (i != j) cur += val[j];
if (sum[i] == k * cur) {
cout << i << '\n'; return 0;
}
}
}
