#include<iostream>
#include<cstdio>
#define syy myson
using namespace std;
int m,n,a[51][51]={0},f[51][51][51][51],i,j,k,l;
inline int max(int a,int b)
{
	return a>b?a:b;
}
inline void input()
{
	scanf("%d%d",&m,&n);
	for(i=1;i<=m;i++)
	  for(j=1;j<=n;j++)
	    scanf("%d",&a[i][j]);
}
inline void work()
{
	for(i=1;i<=m;i++)
	for(j=1;j<=n;j++)
	for(k=1;k<=m;k++)
	for(l=1;l<=n;l++)
		if((i!=k&&j!=l)||(i==1&&j==1&&k==1&&l==1)||(i==m&&j==n&&i==m&&j==n))
			f[i][j][k][l]=max(max(max(f[i-1][j][k-1][l],f[i][j-1][k-1][l]),f[i-1][j][k][l-1]),f[i][j-1][k][l-1])+a[i][j]+a[k][l];
}
inline void output()
{
	printf("%d",f[m][n][m][n]);
}
int Main()
{
	freopen("message.in","r",stdin);freopen("message.out","w",stdout);
	input();
	work();
	output();
	return 0;
}
int main(){;};
int syy=Main();