能过样例

#include<iostream>
using namespace std;
const int N=1e3+5;
int n,m;
int sum[N][N],a[N][N];
int main(){
	cin>>n;
	for (int i=1;i<=n;i++){
		for (int j=1;j<=n;j++){
			cin>>a[i][j];
			sum[i][j]=sum[i-1][j]+sum[i][j-1]-sum[i-1][j-1]+a[i][j];
		}
	}
	int ans=0;
	for (int x1=1;x1<=n;x1++){
		for (int y1=1;y1<=n;y1++){
			for (int x2=x1;x2<=n;x2++){
				for (int y2=y1;y2<=n;y2++){
					ans=max(ans,sum[x2][y2]-sum[x1-1][y2]+sum[x1-1][y1-1]);
				}
			}
		}
	}
	cout<<ans;
	return 0;
}