C++ :

#include<iostream>
#include<algorithm>
#include<string.h>
using namespace std;
const int N(55);
int a[N][N],f[2*N][N][N]={0};
//ifstream cin("message.in");
//ofstream cout("message.out");
int big(int a,int b,int c,int d)
{  return max(max(a,b),max(c,d)); }
int main()
{
    int n,m;
    while (cin>>n>>m)
    {
        memset(f,sizeof(int)*2*N*N*N,0);
        for (int i=1;i<=n;i++)
            for (int j=1;j<=m;j++)
                cin>>a[i][j];
        f[2][1][1]=a[1][1];
        for (int k=3;k<n+m;k++)
            for (int x1=1;x1<n;x1++)
                for (int x2=x1+1;x2<=n;x2++)
                    if (k-x2>=1&&k-x1<=m)
                        f[k][x1][x2]=big(f[k-1][x1-1][x2-1],f[k-1][x1][x2],
                            f[k-1][x1][x2-1],f[k-1][x1-1][x2])+a[x1][k-x1]+a[x2][k-x2];
        cout<<f[n+m-1][n-1][n]<<endl;
    }
    return 0;
}

Java :

import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		int N=55;
		int[][] a = new int[N][N];
		int[][][] f = new int[2*N][N][N];
		Scanner in = new Scanner(System.in);
		int n, m;
		while (in.hasNext())
		{
			n=in.nextInt();
			m=in.nextInt();
			//memset(f,  * 2 * N * N * N, 0);
			for (int i = 1; i <= n; i++)
				for (int j = 1; j <= m; j++)
					a[i][j]=in.nextInt();
			f[2][1][1] = a[1][1];
			for (int k = 3; k < n + m; k++)
				for (int x1 = 1; x1 < n; x1++)
					for (int x2 = x1 + 1; x2 <= n; x2++)
						if (k - x2 >= 1 && k - x1 <= m)
							f[k][x1][x2] = big(f[k - 1][x1 - 1][x2 - 1], f[k - 1][x1][x2],
								f[k - 1][x1][x2 - 1], f[k - 1][x1 - 1][x2]) + a[x1][k - x1] + a[x2][k - x2];
			System.out.println(f[n + m - 1][n - 1][n]);
		}
	}
	static int big(int a, int b, int c, int d)
	{
		if (a < b) a = b;
		if (a < c) a = c;
		if (a < d) a = d;
		return a;
	}
}