#include <iostream>
#include <queue>
#include <string>
#include <algorithm>
#include <vector>
#include <cmath>
#include <iomanip>
#include <map>
#include <cstring>
#include <set>
#define ll long long
#define INF (3001*3001*100)
#define MAX (int) 3100
#define MOD 1000000007
#define par pair<int, int>
#define all(v) v.begin(), v.end()
#define lsb(x) (x & -x)
#define _ ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

using namespace std;

int tab[MAX][MAX], n, m, dp[10][MAX][MAX], vis[MAX][MAX];

int e(int a, int b)
{
    return (a>=0 && b>=0 && a<n && b<m && !vis[a][b]);
}

int f(int d, int a, int b)
{
    if (a == n-1 && b == m-1) return 0;
    if (~dp[d][a][b]) return dp[d][a][b];
    int ans = -INF;

    vis[a][b] = 1;
    if (e(a, b+1)) ans = max(ans, f(1, a, b+1) + tab[a][b+1]);
    if (e(a, b-1)) ans = max(ans, f(2, a, b-1) + tab[a][b-1]);
    if (e(a+1, b)) ans = max(ans, f(3, a+1, b) + tab[a+1][b]);
    vis[a][b] = 0;

    return dp[d][a][b] = ans;
}

int main()
{_
    cin >> n >> m;
    memset(dp, -1, sizeof(dp));
    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++)
            cin >> tab[i][j];

    cout << f(0, 0, 0) + tab[0][0] << endl;
}