#include <iostream>
#include <vector>
#include <set>

/*
3 4
2 2 4 0
1 3 1 0
2 5 3 1
 */

void dfs(std::pair<int, int> pos, std::pair<int, int> endPos, std::set<std::pair<int, int>> & visited,
         int & larvas, int & maxLarvas, std::vector<std::vector<int>> & map) {
    if (pos.first < 0 || pos.second < 0 || pos.first > endPos.first || pos.second > endPos.second || !visited.insert(pos).second)
        return;

    larvas += map[pos.first][pos.second];

    if (pos == endPos) {
        if (larvas > maxLarvas)
            maxLarvas = larvas;
        larvas -= map[pos.first][pos.second];
        visited.erase(pos);
        return;
    }

    dfs({pos.first    , pos.second + 1}, endPos, visited, larvas, maxLarvas, map);
    dfs({pos.first    , pos.second - 1}, endPos, visited, larvas, maxLarvas, map);
    dfs({pos.first + 1, pos.second    }, endPos, visited, larvas, maxLarvas, map);
    dfs({pos.first - 1, pos.second    }, endPos, visited, larvas, maxLarvas, map);

    larvas -= map[pos.first][pos.second];
    visited.erase(pos);
}

int main() {
    int m, n;
    std::cin >> n >> m;
    std::vector<std::vector<int>> map(n);
    int sum = 0;
    int min = 999999;
    for (int i = 0; i < n; ++i) {
        map[i].resize(m);
        for (int j = 0; j < m; ++j)
        {
            std::cin >> map[i][j];
            sum += map[i][j];
            if(j == 0 && i == 0)
                continue;
            if(j == m - 1 && i == n - 1)
                continue;
            if(map[i][j] < min)
                min = map[i][j];
        }
    }

    if(n % 2 == 1 || m % 2 == 1)
    {
        std::cout << sum << std::endl;
        return 0;
    }


    std::cout << sum - min << std::endl;


    //std::set<std::pair<int, int>> visited;
    //int maxLarvas = 0, larvas = 0;
    //dfs({0, 0}, {n - 1, m - 1}, visited, larvas, maxLarvas, map);

    //std::cout << maxLarvas << std::endl;

    return 0;
}