#include <iostream>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <fstream>
#define cin fin
#define cout fout
using namespace std;
ifstream fin("message.in");
ofstream fout("message.out");
const int MAXN = 51;
int f[MAXN][MAXN], dp[MAXN + MAXN][MAXN][MAXN] = {0}, n, m;

int main()
{
   cin>>m>>n;
	for(int i=1;i<=m;i++)
		for(int j=1;j<=n;j++)
			cin>>f[i][j];
	memset(dp,0,sizeof(dp));
for(int st=1;st<=n-1+m-1;st++)
	{
		int t=min(st,m+n-1-1);
		for(int i=1;i<=t;i++)
		{
			int j=st-i+1;
			for(int k=i+1;k<=t;k++)
			{
				int l = st - k + 1, la = st - 1;
				int& ans = dp[st][i][k];
				ans = max(ans, dp[la][i][k]);
				ans = max(ans, dp[la][i][k - 1]);
				ans = max(ans, dp[la][i - 1][k]);
				ans = max(ans, dp[la][i - 1][k - 1]);
				ans += (f[i][j]  + f[k][l]);
			}
		}
	}
	cout << dp[n - 1 + m - 1][m - 1][m] << endl;

	return 0;
}