#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ld = long double;
#define print(x) cerr << #x << " = " << x << endl

template<class T>
ostream& operator<<(ostream &out, vector<T> &cont) {
    out << "[";
    for (const auto &x : cont) out << x << ", ";
    out << "]";
    return out;
}

int32_t main() {
    int n, m;
    cin >> n >> m;
    
    if(n%2 == 0 && m%2 == 0){
        int ans = 0;
        int smallestBad = INT_MAX;
        for(int i=0; i<n; i++){
            for(int j = 0; j<m; j++){   
                int helper;
                cin >> helper;

                if(i+j != 0 &&  !(i == n-1 && j == m-1) && (i+j)%2 == 1){
                    smallestBad = min(smallestBad, helper);
                } 

                ans += helper;
            }
        }
        
        cout << ans - smallestBad << '\n';

    }
    else{
        int ans = 0;
        for(int i=0; i<n*m; i++){
            int helper;
            cin >> helper;
            ans += helper;
        }

        cout << ans << '\n';
    }
}