//
// Created by cteam37 on 10/19/24.
//


#include <iostream>
#include <vector>

using namespace std;

int main() {

    int n,m;
    cin >> n;
    cin >> m;

    ::uint64_t totalSum = 0;
    int min = INT32_MAX;

    for (int i = 0; i < n*m; ++i) {
        int val;
        cin >> val;
        totalSum += val;
        if(i == 0 || i == n*m - 1) {
            continue;
        }
        if (val < min) min = val;

    }

    if(n%2 == 0 && m%2 == 0) {
        cout << totalSum - min << endl;
    } else {
        cout << totalSum << endl;
    }



    return 0;
}