easy dp

//File Name: nod1051.cpp
//Author: long
//Mail: 736726758@qq.com
//Created Time: 2016年05月28日 星期六 21时22分03秒

#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <iostream>

#define LL long long

using namespace std;

const int MAXN = 501;

LL b[MAXN],f[MAXN];
int a[MAXN][MAXN];

LL get(int n){
LL ans = 0;
f[0] = 0;
for(int i=1;i<=n;i++){
f[i] = max(f[i-1],0LL) + b[i];
if(f[i] > ans) ans = f[i];
}
return ans;
}

LL solve(int n,int m){
LL ans = -1;
for(int i=1;i<=n;i++){
for(int j=1;j<=m;j++) b[j] = 0;
for(int j=i;j<=n;j++){
for(int k=1;k<=m;k++)
b[k] = b[k] + a[j][k];
LL now = get(m);
if(now > ans) ans = now;
}
}
return ans;
}

int main(){
int n,m;
while(~scanf("%d %d",&m,&n)){
bool flag = false;
for(int i=1;i<=n;i++){
for(int j=1;j<=m;j++){
scanf("%d",&a[i][j]);
if(a[i][j] >= 0) flag = true;
}
}
if(!flag) puts("0");
else printf("%lld\n",solve(n,m));
}
return 0;
}