#pragma GCC optimize(2, 3, "inline", "Ofast", "unroll-loops")
#include <bits/stdc++.h>
#define M 100005

using namespace std;
string s[M];
int n, m, k, tot[M];
bool check(int x) {
    for (int i = 1; i <= n; i++) {
        if (i == x)
            continue;
        int cnt = 0;
        for (int j = 0; j < m; j++)
            if (s[i][j] != s[x][j])
                cnt++;
        if (cnt != k)
            return 0;
    }
    return 1;
}
signed main() {
    //	freopen("data.in", "r", stdin);
    scanf("%d%d%d", &n, &m, &k);
    for (int i = 1; i <= n; i++) cin >> s[i];
    if (1ll * n * n * m <= 100000000) {
        //		cout << 1ll * n * n * m << endl;
        for (int i = 1; i <= n; i++) {
            if (check(i)) {
                printf("%d\n", i);
                return 0;
            }
        }
    }
    //	cout << 1 << endl;
    for (int i = 0; i < m; i++) {
        static vector<int> v[4];
        v[0].clear(), v[1].clear(), v[2].clear(), v[3].clear();
        for (int j = 1; j <= n; j++) {
            v[s[j][i] - 'A'].push_back(j);
        }
        for (int j = 0; j < 4; j++) {
            int sum = n - v[j].size();
            for (auto t : v[j]) tot[t] += sum;
        }
    }
    for (int i = 1; i <= n; i++) {
        if (tot[i] == (n - 1) * k && check(i)) {
            printf("%d\n", i);
            break;
        }
    }
    return 0;
}