C :

#include<stdio.h>
int m,n,a[51][51];
int f[51][51][51][51];
int my_max(int,int,int,int);
int main()
{
	scanf("%d%d",&n,&m);
	for(int i=1;i<=n;i++)
		for(int j=1;j<=m;j++)
		{
			scanf("%d",&a[i][j]);
		}
		for(int i1=1;i1<=n;i1++)
			for(int j1=1;j1<=m;j1++)
				for(int i2=1;i2<=n;i2++)
					for(int j2=1;j2<=m;j2++)
					{
						f[i1][j1][i2][j2]=my_max(f[i1-1][j1][i2][j2-1],
											  f[i1-1][j1][i2-1][j2],
											  f[i1][j1-1][i2-1][j2],
											  f[i1][j1-1][i2][j2-1]);
						f[i1][j1][i2][j2]+=a[i1][j1];
						if(i1!=i2||j1!=j2)  f[i1][j1][i2][j2]+=a[i2][j2];
					}
		printf("%d",f[n][m][n][m]);
}
int my_max(int a,int b,int c,int d)
{
	int tot=0;
	if(tot<a) tot=a;
	if(tot<b) tot=b;
	if(tot<c) tot=c;
	if(tot<d) tot=d;
	return tot;
}

C++ :

#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;
const int maxn=51;
int m,n,a[maxn][maxn],f[maxn][maxn][maxn][maxn]={0};
int my_max(int,int);
void work();
int main()
{
	//freopen("message3.in","r",stdin);
	work();
	return 0;
}
void work()
{
	cin>>m>>n;
	for(int i=1;i<=m;i++)
		for(int j=1;j<=n;j++)cin>>a[i][j];
	for(int i1=1;i1<=m;i1++)
		for(int j1=1;j1<=n;j1++)
			for(int i2=1;i2<=m;i2++)
				for(int j2=1;j2<=n;j2++)
				if(i1!=i2&&j1!=j2)
				{
					int x=my_max(f[i1-1][j1][i2-1][j2],f[i1][j1-1][i2][j2-1]);
					int y=my_max(f[i1-1][j1][i2][j2-1],f[i1][j1-1][i2-1][j2]);
					f[i1][j1][i2][j2]=my_max(x,y)+a[i1][j1]+a[i2][j2];
					//cout<<i1<<' '<<j1<<' '<<i2<<' '<<j2<<' '<<x<<' '<<y<<endl;
				}
	cout<<my_max(f[m][n-1][m-1][n],f[m-1][n][m][n-1])<<endl;
}
int my_max(int x,int y)
{
	if(x>y)return x;
	else return y;
}

Pascal :

var m,n,i,j,k:integer;
    a:array[1..50,1..50]of integer;
    f:array[1..100,0..50,0..50]of longint;
function max(a,b,c,d:longint):longint;
begin
  max:=-1;
  if a>max then max:=a;
  if b>max then max:=b;
  if c>max then max:=c;
  if d>max then max:=d;
end;
begin
  readln(m,n);
  for i:=1 to m do
    for j:=1 to n do read(a[i,j]);
  for i:=2 to m+n-1 do
   for j:=1 to m do
    for k:=1 to m do
     if (i+1-j>0)and(i+1-k>0) then
       begin
        f[i,j,k]:=max(f[i-1,j-1,k-1],f[i-1,j-1,k],f[i-1,j,k-1],f[i-1,j,k]);
        if (j<>k) then inc(f[i,j,k],a[j,i+1-j]+a[k,i+1-k])
         else inc(f[i,j,k],a[j,i+1-j]);
       end;
  writeln(f[m+n-1,m,m]);
end.