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


#include <iostream>
#include <vector>

using namespace std;

int main() {

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

    int totalSum = 0;
    int min = INT32_MAX;

    vector<vector<int>> fields;

    for (int row = 0; row < n; ++row) {
        fields.push_back({});
        for (int col = 0; col < m; ++col) {
            int val;
            cin >> val;
            fields[row].push_back(val);
            totalSum += val;
            if((row == 0 && col == 0) || (row == n-1 && col == n-1)) {
                continue;
            }
            if (val < min) min = val;
        }
    }

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



    return 0;
}