#include<iostream>
#include<cstdlib>
#include<cstdio>
#include<cctype>
#include<cstring>
using namespace std;
int read()
{
	int x,f=1;
	char ch;
	while(ch=getchar(),!isdigit(ch))if(ch=='-')f=-1;
	x=ch-48;
	while(ch=getchar(),isdigit(ch))x=x*10+ch-48;
	return x*f;
}
int a[110][110],f[210][210][210];
int init()
{
	freopen("message.in","r",stdin);
	freopen("message.out","w",stdout);
	int m=read(),n=read();
	for(int i=1;i<=m;i++)
	{
		for(int j=1;j<=n;j++)
		{
			a[i][j]=read();
		}
	}
	for(int k=1;k<=m+n-2;k++)
	{
		for(int i=1;i<=m;i++)
		{
			for(int j=1;j<=m;j++)
			{
				if(i==j)continue;
				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][j-1]);
				f[k][i][j]=max(f[k][i][j],f[k-1][i-1][j-1]);
				f[k][i][j]=max(f[k][i][j],f[k-1][i][j]);
				f[k][i][j]+=a[i][k+2-i]+a[j][k+2-j];
			}
		}
	}
	int ans=max(f[m+n-3][m][m-1],f[m+n-3][m-1][m]);
	printf("%d",ans);
}
int yyo=init();
int main()
{
	;
}