#include<iostream>
#include<cstdio>
#include<cctype>
#define gys mylove
using namespace std;
int m,n,a[51][51],dp[110][51][51],ans=0;
inline void in(int &x)
{
    x=0;int f=1;char t=getchar();
    while(!isdigit(t)){if(t=='-')f=-1;t=getchar();}
    while(isdigit(t)){x=x*10+t-48;t=getchar();}
    x*=f;
}
inline void work(){
	in(n);in(m);
	for(int i=1;i<=n;i++)
	 for(int j=1;j<=m;j++) in(a[i][j]);
	for(int i=1;i<=m+n-1;i++)
	 for(int x=1;x<=n;x++)
	  for(int y=1;y<=n;y++){
	  	if(x==y) continue;
	  	dp[i][x][y]=max(max(dp[i-1][x][y],dp[i-1][x-1][y]),max(dp[i-1][x][y-1],dp[i-1][x-1][y-1]))+a[x][i+1-x]+a[y][i+1-y];
	  	ans=max(ans,dp[i][x][y]);
	  }
	printf("%d",ans);
}
inline int Main(){
	freopen("message.in","r",stdin);
	freopen("message.out","w",stdout);
	work();
	return 0;
}
int main(){;}
int gys=Main();