#include <bits/stdc++.h>
using namespace std;
#define int long long
const int mod = (1LL << 31) - 1;
mt19937 rng((int) chrono::steady_clock::now().time_since_epoch().count());
int rnd(int u, int v) {
return uniform_int_distribution<int> (u, v) (rng);
}
int cv(char x) {
if (x == 'A') return 0;
if (x == 'C') return 1;
if (x == 'G') return 2;
return 3;
}
int32_t main() {
ios::sync_with_stdio(0); cin.tie(0);
int n, m, diff;
cin >> n >> m >> diff;
vector<int> w(n);
vector<vector<int>> c(m, vector<int> (4, 0));
vector<string> a(n);
for (int i = 0; i < n; i++) {
cin >> a[i];
w[i] = rnd(1, (1LL << 31) - 2);
for (int j = 0; j < m; j++) c[j][cv(a[i][j])] = (c[j][cv(a[i][j])] + w[i]) % mod;
}
for (int i = 0; i < n; i++) {
int wc = 0, sum = 0;
for (int j = 0; j < n; j++) {
if (i == j) continue;
sum = (sum + w[j]) % mod;
}
sum = (sum * diff) % mod;
for (int j = 0; j < m; j++) {
for (int k = 0; k < 4; k++) if (cv(a[i][j]) != k) wc = (wc + c[j][k]) % mod;
}
if (sum != wc) continue;
cout << i + 1 << '\n';
return 0;
}
}
