#include <bits/stdc++.h>
using namespace std;
int main() {
cin.tie(0)->sync_with_stdio(0);
int n, m, k; cin >> n >> m >> k;
vector<string> seq(n); for (int i = 0; i < n; i++) cin >> seq[i];
using b = bitset<4100>;
vector<b> s2(n);
for (int i = 0; i < n; i++) for (int j = 0; j < m; j++) if (seq[i][j] == 'A') s2[i][j] = 1;
vector<int> cnt(n);
for (int i = 0; i < n; i++) {
for (int j = i+1; j < n; j++) {
int t = (s2[i] ^ s2[j]).count();
// int t = 0;
// for (int k = 0; k < m; k++) {
// if (seq[i][k] != seq[j][k]) t++;
// }
if (t == k) cnt[i]++, cnt[j]++;
}
if (cnt[i] == n-1) {
cout << i+1 << "\n";
break;
}
}
return 0;
}
