#pragma GCC optimize("O3", "unroll-loops")
#pragma GCC target("avx", "avx2", "popcnt")
#include <bits/stdc++.h>
using namespace std;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int Z = 4100;
int N, M, K;
bitset<Z*4> a[Z];
int g[100];
bool chk[Z][Z]; int cnt[Z][Z];
int main() {
ios::sync_with_stdio(0), cin.tie(0);
g['C'] = 1;
g['G'] = 2;
g['T'] = 3;
cin >> N >> M >> K;
vector<int> o(N);
for(int i = 0; i < N; ++i) {
string inp; cin >> inp;
for(int j = 0; j < M; ++j)
a[i][g[int(inp[j])] * Z + j] = 1;
o[i] = i;
}
shuffle(begin(o), end(o), rng);
for(const int &i : o) {
bool ok = 1;
a[i].flip();
for(int j = 0; j < N; ++j) if(i != j) {
int c = (chk[i][j] ? cnt[i][j] : (a[i] & a[j]).count());
chk[j][i] = 1;
cnt[j][i] = c;
if(c != K) {
ok = 0;
break;
}
}
if(ok) {
cout << i + 1;
return 0;
}
a[i].flip();
}
}
