#include <bits/stdc++.h>
using namespace std; 
const char ch[] = "ATGC";
const int N = 4105, T = 30; 

int n, m, k, sz[T + 5], cnt[T + 5][N + 5][4], b[N + 5];
int str[N + 5][N + 5];
char s[N + 5];
bool ok[N + 5]; 
mt19937 Rand(time(0)); 

int main(void) {
    ios::sync_with_stdio(0); 
    cin >> n >> m >> k; 
    for (int i = 1; i <= n; ++i) {
        cin >> s; ++sz[b[i] = rand() % T]; 
        for (int j = 0; j < m; ++j)
            for (int o = 0; o < 4; ++o)
                if (ch[o] == s[j]) {
                    ++cnt[b[i]][j][o];
                    str[i][j] = o;
                    break;
                }
    }
    for (int i = 1; i <= n; ++i) {
        bool flag = true;
        for (int o = 0; o < T; ++o) {
            int t = (m - k) * sz[o];
            if (b[i] == o) t += k; 
            for (int j = 0; j < m; ++j) t -= cnt[o][j][str[i][j]]; 
            if (t) { flag = 0; break; }
        }
        if (flag) return cout << i << "\n", 0; 
    }
    return 0;
}