#include <bits/stdc++.h>
using namespace std;
typedef long long i64;
const int N = 4105;

mt19937 Rand(time(0));

int n, m, k, opt[128]; 
char s[N][N]; 
i64 cnt[N][4], w[N], sum;

int main(void) {
    opt['A'] = 0, opt['G'] = 1, opt['T'] = 2, opt['C'] = 3;
    scanf("%d%d%d", &n, &m, &k); 
    for (int i = 1; i <= n; ++i) {
        scanf("%s", s[i] + 1), w[i] = Rand(); 
        for (int j = 1; j <= m; ++j) cnt[j][opt[s[i][j]]] += w[i]; 
        sum += w[i];
    }
    for (int i = 1; i <= n; ++i) {
        i64 res = 0;
        for (int j = 1; j <= m; ++j)
            for (int k = 0; k < 4; ++k) {
                if (opt[s[i][j]] == k) continue; 
                res += cnt[j][k];
            }
        if (res == (sum - w[i]) * k) return cout << i << "\n", 0; 
    }
    return 0;
}