acwing 275

#include <bits/stdc++.h>

using namespace std;

const int N = 60;
int g[N][N];
int f[N + N][N][N];
int n, m;

int main()
{
    cin >> n >> m;
    for (int i = 1; i <= n; i ++)
        for (int j = 1; j <= m; j ++) cin >> g[i][j];
    
    memset(f, 0, sizeof f);
    
    
    
    for (int k = 2; k <= n + m; k ++)
        for (int x1 = max(1, k - m); x1 <= min(n, k - 1); x1 ++)
            for (int x2 = max(1, k - m); x2 <= min(n, k - 1); x2 ++)
            {
                int y1 = k - x1, y2 = k - x2;
                int t = g[x1][y1];
                if (x1 != x2) t += g[x2][y2];
                for (int a = 0; a <= 1; a ++)
                    for (int b = 0; b <= 1; b ++) 
                    {
                        f[k][x1][x2] = max(f[k][x1][x2], f[k-1][x1-a][x2-b] + t);
                    }
            }
            
    printf("%d", f[n+m][n][n]);
    return 0;
}