Code：

#include <bits/stdc++.h>
using namespace std;
int mp[102][102];
int cntblack(int l, int u, int r, int d){
    int sum = 0;
    for (int i = l; i <= r; i++){
        for (int j = u; j < d; j++){
            sum += mp[i][j];
        }
    }
    return sum;
}
int main(){
    int n, m, k;
    cin >> n >> m >> k;
    for (int i = 1; i <= n; i++){
        for (int j = 1; j <= m; j++){
            cin >> mp[i][j];
        }
    }
    if (cntblack(1, 1, n, m) < k){
        printf("0");
        return 0;
    }
    int ans = 0, K = 1, l = 1;
    for (int i = 1; i <= n; i++){
        for (int j = 1; j <= m; j++){
            for (K = 1; K <= n - i; K++){
                for (l = 1; l <= m - j; l++){
                    ans = max(ans, cntblack(i, j, i+k, j+l));
                }
            }
        }
    }
    printf("%d", ans);
    return 0;
}