#include <bits/stdc++.h>

using namespace std;

#define ll long long

int main(){
    int r, c;
    cin >> r >> c;

    ll res = 0;
    vector<vector<ll>> grid;
    for(int i = 0; i < r; i++){
        grid.push_back({});
        for(int j = 0; j < c; j++){
            ll a;
            cin >> a;
            res += a;
            grid[i].push_back(a);
        }
    }
    if(r % 2 != 0 || c % 2 != 0){
        cout << res << endl;
        return 0;
    }


    ll best = 0;
    for(int i = 0; i < r; i++){
        int start = i % 2 == 1 ? 0 : 1;
        for(int y = start; y < c; y+=2){
            if((i == 0 && y ==0 ) || (i == r - 1 && y == c -1)) continue;
            best = max(best, res - grid[i][y]);
        }
    }
    cout << best << endl;

}