#include <iostream>

using namespace std;
const int N = 60;
int a[N][N];
int dp[N][N][N][N];
int main(){
	int n, m;
	cin >> n >> m;
	for(int i = 1; i <= n; i++){
		for(int j = 1; j <= m; j++){
			cin >> a[i][j];
		}
	}
	for(int i = 1; i <= n; i++){
		for(int j = 1; j <= m; j++){
			for(int x = 1; x <= n; x ++){
				for(int y = 1; y <= m; y++){
					int *t;
					t = &dp[i][j][x][y];
					*t = max(*t, dp[i-1][j][x][y-1]);
					*t = max(*t, dp[i-1][j][x-1][y]);
					*t = max(*t, dp[i][j-1][x-1][y]);
					*t = max(*t, dp[i][j-1][x][y-1]);
					*t += a[i][j] + a[x][y];
					if(i == x && j == y)
						*t -= a[x][y];
				}
			}
		}
	
	}
	cout << dp[n][m][n][m];
} 

#include<bits/stdc++.h>
using namespace std;
const int N=55;
int m,n,a[N][N],dp[N][N][N];
int main(){
    cin>>m>>n;
    for(int i=1;i<=m;i++){
        for(int j=1;j<=n;j++){
            cin>>a[i][j];
        }
    }
    for(int i=1;i<=m;i++)
        for(int j=1;j<=n;j++)
            for(int k=1;k<=m;k++){
                int l=i+j-k;
                if(l>=1&&l<=n) {
                    int temp=max(max(dp[i-1][j][k-1],dp[i-1][j][k]),max(dp[i][j-1][k-1],dp[i][j-1][k]));
                    dp[i][j][k]=temp+a[i][j];
                    if(i!=k) dp[i][j][k]+=a[k][l];
                }
            }
    cout<<dp[m][n][m]<<endl;
    return 0;
}

C++ :

#include<bits/stdc++.h>
using namespace std;
int a[51][51],n,m;
unsigned int s[51][51][51][51];
int main(int argc,char*argv[]){
    memset(a,0,sizeof(a));
    memset(s,0,sizeof(s));
    scanf("%d%d",&m,&n);
    for(int i=1;i<=m;i++){
    	for(int j=1;j<=n;j++){
    		 scanf("%d",&a[i][j]); 
		}   
		int a1,a2;
    	for(int j=1;j<=n;j++){
    		for(int k=1;k<=m;k++){
    			for(int l=1;l<=n;l++){
            		a1=max(s[i][j-1][k][l-1],s[i-1][j][k][l-1]);
            		a2=max(s[i-1][j][k-1][l],s[i][j-1][k-1][l]);
            		s[i][j][k][l]=max(a1,a2)+a[i][j]+a[k][l];
            		if(i==k&&j==l)s[i][j][k][l]-=a[i][j];
        		}
			}
		}
	}
    printf("%d",s[m][n][m][n]);
    return 0;
}