#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 1e5 + 5;
string str[MAX_N];
int N, M, K;
int buc[MAX_N][4];
using LL = long long;
bool check(int p) {
	for (int i = 1; i <= N; i++) {
		if (i == p) continue;
		int cnt = 0;
		for (int j = 0; j < M && cnt <= K; j++)
			cnt += str[p][j] != str[i][j];
		if (cnt != K) return 0;
	}
	return 1;
}
int main() {
	ios::sync_with_stdio(false);
	cin >> N >> M >> K;
	for (int i = 1; i <= N; i++) cin >> str[i];
	for (int i = 1; i <= N; i++)
		for (int j = 0; j < M; j++)
			buc[j][str[i][j] - 'A']++;
	for (int i = 1; i <= N; i++) {
		LL sum = 0;
		for (int j = 0; j < M; j++)
			sum += N - buc[j][str[i][j] - 'A'];
		if (sum == 1ll * (N - 1) * K) {
			if (check(i)) {
				cout << i << endl;
				return 0;
			}
		}
	}
	return 0;
}