WA in #6 #14 #18 #22

#include<bits/stdc++.h>
#define N 1010
#define int long long
using namespace std;
int f[N][N],a[N][N],n,m,ans = LONG_LONG_MAX;
signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0),cout.tie(0);
	cin >> n >> m;
	for(int i = 1;i <= n;i ++)
	for(int j = 1;j <= m;j ++)
	{
		cin >> a[i][j];
		a[i][j] += (a[i][j - 1] >= 0 ? 0 : a[i][j - 1]);
		f[i][j] = ans;
	}
	for(int i = 1;i <= m;i ++) f[n + 1][i] = 0;
	for(int i = 1;i <= n;i ++) f[i][m + 1] = 0;
	for(int i = n;i > 0;i --)
	for(int j = m;j > 0;j --)
	f[i][j] = min(f[i + 1][j] + (a[i][j] < 0 ? a[i][j] : 0),f[i][j + 1]) + (a[i][j] >= 0 ? a[i][j] : 0);
	for(int i = 1;i <= m;i ++) ans = min(ans,f[1][i]);
	cout << ans << endl;
	return 0;
}