#include <iostream>
#include <vector>

using namespace std;

int main() {
    int N, M;
    cin >> N >> M;
    int smallestAtWall = 10000;
    int s1 = 10000;
    int s2 = 10000;
    int s3 = 10000;

    long long sum = 0;
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < M; j++) {
            int temp;
            cin >> temp;
            sum += temp;
            if (i == 0 || j == 0 || (j == M-1) || (i == N-1)) {
                if (!(i == 0 && j == 0) && !(i == N-1 && j == M-1)) {
                    smallestAtWall = min(smallestAtWall, temp);
                }
            } else {
                if (temp < s1) {
                    s3 = s2;
                    s2 = s1;
                    s1 = temp;
                }
                else if (temp < s2) {
                    s3 = s2;
                    s2 = temp;
                }
                else if (temp < s3) {
                    s3 = temp;
                }
            }
        }
    }

    if (M%2 || N%2) {
        cout << sum << endl;
    } else {
        if (s1 + s2 < smallestAtWall) {
            cout << (sum - s1 - s2) << endl;
        } else {
            cout << (sum - smallestAtWall) << endl;
        }
    }
}