#include <bits/stdc++.h>
#define int long long
using namespace std;
void solve(){
    ios::sync_with_stdio(0);
    cin.tie(NULL);
    cout.tie(NULL);

    int n,m;
    cin >> n >> m;
    
    vector<vector<int>>s;
    s.resize(n + 1,vector<int>(m + 1));
    for(int i = 1;i <= n;i++){
        for(int j = 1;j <= m;j++){
            cin >> s[i][j];
        }
    }
    
    vector<vector<vector<int>>>dp;
    dp.resize(n + 1,vector<vector<int>>(m + 1,vector<int>(3 + 1,-1e18)));
    dp[1][1][1] = dp[1][1][2] = dp[1][1][3] = s[1][1];
    for(int j = 1;j <= m;j++){
        for(int i = 1;i <= n;i++){
            dp[i][j][1] = max({dp[i][j - 1][1],dp[i][j - 1][2],dp[i][j - 1][3]}) + s[i][j];
        }
        for(int i = 2;i <= n;i++){
            dp[i][j][2] = max(dp[i - 1][j][1],dp[i - 1][j][2]) + s[i][j];
        }
        for(int i = n - 1;i >= 1;i--){
            dp[i][j][3] = max(dp[i + 1][j][3],dp[i + 1][j][1]) + s[i][j];
        }
    }
    cout << max({dp[n][m][1],dp[n][m][2],dp[n][m][3]}) << "\n";
    return;
}
signed main(){
    int T = 1;
    while(T--){
        solve();
    }
    return 0;
}