/*
Genetics
https://oj.uz/problem/view/BOI18_genetics
*/
#include <bits/stdc++.h>
#include <ext/random>
using namespace std;
const int N = 4100;
int h[256];
__gnu_cxx::sfmt19937 rng(1234);
int main() {
ios::sync_with_stdio(0), cin.tie(0);
h['A'] = 0, h['C'] = 1, h['G'] = 2, h['T'] = 3;
int n, m, k; cin >> n >> m >> k;
static string s[N];
static long long v[N], f[N][4];
long long u = 0;
for (int i = 0; i < n; i++) {
cin >> s[i], v[i] = rng(), u += v[i];
for (int j = 0; j < m; j++) f[j][h[(int) s[i][j]]] += v[i];
}
for (int i = 0; i < n; i++) {
long long t = 0;
for (int j = 0; j < m; j++) t += f[j][h[(int) s[i][j]]] - v[i];
if (t == 1LL * (u - v[i]) * (m - k)) {
cout << i + 1 << '\n';
return 0;
}
}
assert(false);
return 0;
}
