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

struct Field {
    int width, height;
    std::pair<int, int> end;
    std::vector<std::vector<int>> field;

    Field(int width, int height) {
        field.reserve(height);
        this->width = width;
        this->height = height;
        end = {width - 1, height -1};
    }

    bool isValidPos(std::pair<int, int> pos) {
        return !(pos.first < 0 || pos.second < 0 || pos.first >= width || pos.second >= height);
    }

    int operator[](const std::pair<int, int> &pos) {
        return field[pos.second][pos.first];
    }
};


int dfs(Field &field, std::set<std::pair<int, int>> &seen, std::pair<int, int> pos, int sum) {
    int value = field[pos];
    if (pos == field.end)
        return sum + value;

    seen.insert(pos);

    int max = 0;
    for (int i = 0; i < 4; i++) {
        auto new_pos = pos;
        switch (i) {
            // UP
            case 0:
                new_pos.second -= 1;
                break;
            // DOWN
            case 1:
                new_pos.second += 1;
                break;
            // LEFT
            case 2:
                new_pos.first -= 1;
                break;
            // RIGHT
            case 3:
                new_pos.first += 1;
                break;
        }

        if (!field.isValidPos(new_pos) || seen.contains(new_pos))
            continue;

        int res = dfs(field, seen, new_pos, sum + value);
        max = std::max(res, max);
    }

    seen.erase(pos);
    return max;
}

int main() {
    int height, width;
    std::cin >> height >> width;

    Field field = Field(width, height);

    int full_sum = 0;
    std::vector<int> sums;
    sums.reserve(height);

    for (int h = 0; h < height; h++) {
        std::vector<int> row;
        row.reserve(width);

        int sum = 0;

        int num;
        for (int w = 0; w < width; w++) {
            std::cin >> num;
            sum += num;
            row.push_back(num);
        }

        full_sum += sum;
        sums.push_back(sum);

        field.field.emplace_back(row);
    }

    int res = full_sum;
    if (height % 2 == 0 && width % 2 == 0) {
        std::set<std::pair<int, int>> seen;
        res = dfs(field, seen, {0,0}, 0);
    }

    std::cout << res << std::endl;

    return 0;
}