#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
using namespace std;
int read(){int z=0,mark=1;  char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')mark=-1;  ch=getchar();}
	while(ch>='0'&&ch<='9'){z=(z<<3)+(z<<1)+ch-'0';  ch=getchar();}
	return z*mark;
}
int m,n,a[110][110];
int f[51][51][51][51];
int fx[2]={-1,0},fy[4]={0,-1};
int main(){
	//freopen("ddd.in","r",stdin);
	freopen("message.in","r",stdin);
	freopen("message.out","w",stdout);
	memset(f,0,sizeof(f));
	cin>>m>>n;
	for(int i=1;i<=m;i++)
		for(int j=1;j<=n;j++)
			a[i][j]=read();
	for(int i=1;i<=m;i++)
		a[i][0]=-999999999;
	for(int i=1;i<=n;i++)
		a[0][i]=-999999999;
	for(int i=1;i<=m;i++)
		for(int j=1;j<=n;j++)
			for(int p=1;p<=m;p++)
				for(int q=1;q<=n;q++){
					f[i][j][p][q]=max(f[i][j][p][q],f[i-1][j][p-1][q]);
					f[i][j][p][q]=max(f[i][j][p][q],f[i-1][j][p][q-1]);
					f[i][j][p][q]=max(f[i][j][p][q],f[i][j-1][p-1][q]);
					f[i][j][p][q]=max(f[i][j][p][q],f[i][j-1][p][q-1]);
					f[i][j][p][q]+=a[i][j];
					if(i!=p||j!=q)
						f[i][j][p][q]+=a[p][q];
					//cout<<f[i][j][p][q]<<" ";
				}
	cout<<f[m][n][m][n]<<endl;
	return 0;
}