#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> s1(n), s2(n), s3(n), s4(n);
for (int i = 0; i < n; i++) for (int j = 0; j < m; j++) {
if (seq[i][j] == 'A') s1[i][j] = 1;
if (seq[i][j] == 'T') s2[i][j] = 1;
if (seq[i][j] == 'C') s3[i][j] = 1;
if (seq[i][j] == 'G') s4[i][j] = 1;
}
vector<int> cnt(n);
vector<int> idx(n); iota(idx.begin(), idx.end(), 0);
mt19937 rng(chrono::system_clock::now().time_since_epoch().count());
shuffle(idx.begin(), idx.end(), rng);
for (int I = 0; I < n; I++) {
int i = idx[I];
for (int J = I+1; J < n; J++) {
int j = idx[J];
int t = 0;
t += (s1[i] ^ s1[j]).count();
t += (s2[i] ^ s2[j]).count();
t += (s3[i] ^ s3[j]).count();
t += (s4[i] ^ s4[j]).count();
if (t == 2*k) cnt[i]++, cnt[j]++;
}
if (cnt[i] == n-1) {
cout << i+1 << "\n";
break;
}
}
return 0;
}
