#include <algorithm>
#include <limits>
#include <cstdio>
#include <iostream>

using namespace std;
using u64 = long long;

int hamster[1001][1001];

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

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

    u64 sum = 0;
    int smallest = std::numeric_limits<int>::max();

    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) {
            cin >> hamster[i][j];
            sum += hamster[i][j];

            if (!((i == 0 && j == 0) || (i == n - 1 && j == m - 1))) {
                smallest = std::min(smallest, hamster[i][j]);
            }
        }
    }

    if (n % 2 == 1 || m % 2 == 1) {
        printf("%llu\n", sum);
        return 0;
    }

    sum -= smallest;
    printf("%llu\n", sum);
}