#include <bits/stdc++.h>
using namespace std;
using ll = long long;
mt19937 rng((ll)new char);
string str = "ACTG";
void solve() {
int n, m, k;
cin >> n >> m >> k;
string s[n];
for (int i = 0; i < n; i++) cin >> s[i];
// solve
ll h[n], sum = 0;
for (int i = 0; i < n; i++) sum += h[i] = rng();
ll sm[m][4] = {};
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
for (int c = 0; c < 4; c++) {
if (s[i][j] == str[c]) {
sm[j][c] += h[i];
}
}
}
}
for (int i = 0; i < n; i++) {
ll cur = 0;
for (int j = 0; j < m; j++) {
for (int c = 0; c < 4; c++) {
if (s[i][j] != str[c]) cur += sm[j][c];
}
}
ll want = (sum - h[i]) * k;
if (cur == want) {
cout << i+1 << '\n';
return;
}
}
}
signed main() {
cin.tie(0)->sync_with_stdio(0);
solve();
}
