#include <bits/stdc++.h>
using namespace std;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
int N, M, K;
cin >> N >> M >> K;
const int MAX = 4105;
vector<vector<bitset<MAX>>> A(4, vector<bitset<MAX>>(N, 0));
for (int i = 0; i < N; i++) {
string s;
cin >> s;
for (int j = 0; j < M; j++) {
if (s[j] == 'A') A[0][i][j] = 1;
if (s[j] == 'C') A[1][i][j] = 1;
if (s[j] == 'T') A[2][i][j] = 1;
if (s[j] == 'G') A[3][i][j] = 1;
}
}
bitset<MAX> candidates = 0;
for (int i = 0; i < N; i++) {
candidates[i] = 1;
}
mt19937 rnd(MAX);
vector<int> ord(N);
iota(begin(ord), end(ord), 0);
while (candidates.count() > 1) {
shuffle(begin(ord), end(ord), rnd);
for (int i = 0; i + 1 < N; i++) {
int x = ord[i + 0];
int y = ord[i + 1];
int differ = M;
for (int j = 0; j < 4; j++) {
differ -= (A[j][x] & A[j][y]).count();
}
if (differ != K) {
candidates[x] = 0;
candidates[y] = 0;
}
}
}
cout << (candidates._Find_first() + 1) << '\n';
return 0;
}
