#include <bits/stdc++.h>
using namespace std;
int n,a[1005][1005],m,f[51][51][51][51];
int main(){
	cin >> n >> m;
	for(int i = 1;i <= n;i++){
		for(int j = 1;j <= m;j++){
			cin >> a[i][j];
		}
	}
	for(int i = 1;i <= n;i++){
		for(int j = 1;j <= m;j++){
			for(int k = 1;k < i;k++){
				int l = i+j-k;
				f[i][j][k][l] = max(max(f[i-1][j][k-1][l],f[i-1][j][k][l-1]),max(f[i][j-1][k-1][l],f[i][j-1][k][l-1]))+a[i][j]+a[k][l];
			}
		}
	}
	cout << f[n][m-1][n-1][m];
	return 0;
}