90pts求助,没有long long问题,WA

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int N=1451,limit_less=-19198100;
int n,m;
long long map[N][N],res[N][N][2];
int dfs(int x,int y,bool from){
    if(x<0||y<0||x>=n||y>=m)return limit_less;
    if(res[x][y][from]!=limit_less)return res[x][y][from];
    if(!from)   res[x][y][from]=max(dfs(x+1,y,0),max(dfs(x,y-1,1),dfs(x,y-1,0)))+map[x][y];
    else        res[x][y][from]=max(dfs(x-1,y,1),max(dfs(x,y-1,1),dfs(x,y-1,0)))+map[x][y];
    return      res[x][y][from];
}
int main(){
    scanf("%d%d",&n,&m);
    for(int i=0;i<n;++i){
        for(int j=0;j<m;++j){
            scanf("%d",&map[i][j]);
            res[i][j][0]=res[i][j][1]=limit_less;
        }
    }
    res[0][0][0]=res[0][0][1]=map[0][0];
    printf("%d\n",max(dfs(n-1,m-1,0),dfs(n-1,m-1,1)));
    return 0;
}