#include <iostream>
#include <vector>
#ifdef LOCAL
#include "print.h"
#else
template <typename... Args> inline void print(const Args&... args) {}
inline void newline() {}
#endif
using ll = long long;
#define endl '\n'
#define FOR(i, n) for (int i = 0; i < n; i++)
using namespace std;
struct Position {
int A, C, G, T;
};
signed main() {
ios::sync_with_stdio(0);
cin.tie(0);
#ifdef LOCAL
freopen("input.txt", "r", stdin);
#endif
int n, m, k;
cin >> n >> m >> k;
vector<string> clones(n);
vector<Position> positions(m);
FOR(i, n) {
cin >> clones [i];
FOR(j, m) {
if (clones [i][j] == 'A') {
positions [j].A++;
}
else if (clones [i][j] == 'C') {
positions [j].C++;
}
else if (clones [i][j] == 'G') {
positions [j].G++;
}
else if (clones [i][j] == 'T') {
positions [j].T++;
}
}
}
FOR(i, n) {
int count = 0;
FOR(j, m) {
if (clones [i][j] == 'A') {
count += positions [j].A;
}
else if (clones [i][j] == 'C') {
count += positions [j].C;
}
else if (clones [i][j] == 'G') {
count += positions [j].G;
}
else if (clones [i][j] == 'T') {
count += positions [j].T;
}
count--;
}
if (count == (n - 1) * (m - k)) {
cout << i + 1 << endl;
break;
}
}
}
