C++ :

#include<iostream>
#include<algorithm>
using namespace std;
const int N = 55;
int a[N][N],f[2*N][N][N];

int main(){
	int m,n;
	cin>>m>>n;
	for (int i=1; i<=m; i++)
		for (int j=1; j<=n; j++) cin>>a[i][j];
	for (int k=3; k<m+n; k++)
		for (int x1=1; x1<m; x1++)
			for (int x2=x1+1; x2<=m; x2++)
				if (k-x1>1 && k-x1<=n && k-x2>=1 && k-x2<n)
				{
					f[k][x1][x2]=max(f[k][x1][x2],f[k-1][x1][x2]);
					f[k][x1][x2]=max(f[k][x1][x2],f[k-1][x1][x2-1]);
					f[k][x1][x2]=max(f[k][x1][x2],f[k-1][x1-1][x2]);
					f[k][x1][x2]=max(f[k][x1][x2],f[k-1][x1-1][x2-1]);
					f[k][x1][x2]+=a[x1][k-x1]+a[x2][k-x2];
				}
	cout<<f[m+n-1][m-1][m]<<endl;
	return 0;
}

Pascal :

var
  f:array[-50..101,-50..51,-50..51]of longint;
  a:array[-100..100,-100..100]of longint;
  n,i,j,k,m,maxn,s,minn,xxx:longint;
function max(a,b:longint):longint;
 begin
if a>b then max:=a else max:=b
end;
begin
{assign(input,'message.in');   reset(input);
 assign9output,'message.out'); rewrite(output);}
  readln(n,m);
  for i:=1 to n do
   for j:=1 to m do read(a[i,j]);      fillchar(f,sizeof(f),0);
  xxx:=m+n-2;
  for k:=2 to xxx do
   begin

     for i:=1 to n do
      for j:=i+1 to n do
        begin
          if abs(j-i) > 1 then
           begin
              f[k,i,j]:=max(f[k-1,i,j],f[k-1,i,j-1]);
              f[k,i,j]:=max(f[k,i,j],f[k-1,i-1,j]);
              f[k,i,j]:=max(f[k,i,j],f[k-1,i-1,j-1]);
              inc(f[k,i,j],a[i,k+1-i]+a[j,k+1-j]);
           end else

           begin
             f[k,i,j]:=max(f[k-1,i,j],f[k-1,i-1,j-1]);
             f[k,i,j]:=max(f[k,i,j],f[k-1,i-1,j]);
              inc(f[k,i,j],a[i,k+1-i]+a[j,k+1-j]);
           end;

        end;
   end;
  writeln(f[xxx,n-1,n]);
{close(input); rewrite(output);}
end.