#include<iostream>
#include<algorithm>
using namespace std;

typedef long long ll;
const int MAXN = 1005;
ll a[MAXN][MAXN], sum[MAXN][MAXN];
int n, m, s;

ll S(int x, int y) {
	int x2 = x + m - 1, y2 = y + m - 1;
	return sum[x2][y2] - sum[x - 1][y2] - sum[x2][y - 1] + sum[x - 1][y - 1];
}

bool check(int x1, int y1, int x2, int y2){
	int x1r = x1 + m - 1, y1b = y1 + m - 1;
	int x2r = x2 + m - 1, y2b = y2 + m - 1;
	return x1r < x2 || x2r < x1 || y1b < y2 || y2b < y1;
}

int main(){
    freopen("zfx.in", "r", stdin);
    freopen("zfx.out", "w", stdout);
    ios::sync_with_stdio(0);
    cin.tie(0);
    cin >> n >> m;
	s = n - m + 1;
	if(s < 3){
		cout << 0 << '\n';
		return 0;
	}
	for(int i = 1;i <= n;i ++){
		ll res = 0;
		for(int j = 1;j <= n;j ++){
		    cin >> a[i][j];
			res += a[i][j];
			sum[i][j] = sum[i - 1][j] + res;
		}
	}
	ll maxx = 0;
	for(int x1 = 1;x1 <= s;x1 ++){
	    for(int y1 = 1;y1 <= s;y1 ++){
			ll s1 = S(x1, y1);
			for(int x2 = 1;x2 <= s;x2 ++){
			    for(int y2 = 1;y2 <= s;y2 ++){
					if(!check(x1, y1, x2, y2)) continue;
					ll s2 = S(x2, y2);
					for(int x3 = 1;x3 <= s;x3 ++){
					    for(int y3 = 1;y3 <= s;y3 ++){
							if(!check(x1, y1, x3, y3) || !check(x2, y2, x3, y3)) continue;
							maxx = max(maxx, s1 + s2 + S(x3, y3));
						}
                    }
				}
            }
		}
    }
    cout << maxx << '\n';
	return 0;
}