#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
using namespace std;
const int N = 50+10;
int n,m;
int f[N][N][N+N];
int a[N][N];
inline int read()
{
int x=0,f=1;char ch=getchar();
while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}
while(ch>='0'&&ch<='9')x=(x<<1)+(x<<3)+(ch^48),ch=getchar();
return x*f;
}
int main()
{
// freopen("note.in","r",stdin);
// freopen("note.out","w",stdout);
n=read();m=read();
for(int i=1;i<=n;i++)
for(int j=1;j<=m;j++)a[i][j]=read();
for(int r=1;r<=n+m-2;r++)
for(int i=1;i<=r+1&&i<=n;i++)
for(int j=1;j<=r+1&&j<=n;j++)
{
int xi=i,yi=r+2-i,xj=j,yj=r+2-j;
int dlt=0;
if(xi==xj&&yi==yj)dlt=a[xi][yi];
else dlt=a[xi][yi]+a[xj][yj];
f[i][j][r]=max(f[i][j][r],f[i-1][j][r-1]);
f[i][j][r]=max(f[i][j][r],f[i][j-1][r-1]);
f[i][j][r]=max(f[i][j][r],f[i-1][j-1][r-1]);
f[i][j][r]=max(f[i][j][r],f[i][j][r-1]);
f[i][j][r]+=dlt;
}
printf("%d\n",f[n][n][n+m-2]);
return 0;
}