#include <iostream>
#include <vector>

using namespace std;

int main() {
    int N, M;
    cin >> N >> M;
    int smallestAtWall = 10000;
    int minSum = 10000;

    vector<vector<int>> map(N, vector<int>(M));

    long long sum = 0;
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < M; j++) {
            int temp;
            cin >> temp;
            map[i][j] = temp;
            sum += temp;
            if (i == 0 || j == 0 || i == N-1 || j == M-1) {
                if ((i == 0 && j == 0) || (i == N-1 && j == M-1)) continue;
                smallestAtWall = min(smallestAtWall, temp);
            }
        }
    }

    for (int i = 2; i < N; i+=2) {
        for (int j = 2; j < M; j+=2) {
            if (map[i][j] + map[i][j-1] < minSum) minSum = map[i][j] + map[i][j-1];
            if (map[i][j] + map[i-1][j] < minSum) minSum = map[i][j] + map[i-1][j];
        }
    }


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