#include <iostream>
#include <map>
#include "queue"
#include <set>

struct Hamster {
    int rows;
    int cols;
    std::map<std::pair<int, int>, int> map;

    Hamster(int rows, int cols, const std::map<std::pair<int, int>, int>& map) {
        this->map = map;
        this->rows = rows;
        this-> cols = cols;
    }

    int bfs() {
        int res = 0;
        std::queue<std::pair<int, std::pair<int, int>>> queue;
        std::set<std::pair<int, int>> visited;
        std::vector<std::pair<int, int>> pos = {{-1, 0}, {0, -1}, {1, 0}, {0, 1}};
        queue.push({map[{0, 0}], {0,0}});
        visited.insert({0,0});
        while (!queue.empty()) {
            auto el = queue.front();
            int posX = el.second.first;
            int posY = el.second.second;
            queue.pop();
            if (posX == rows-1 && posY == cols-1) {
                if (el.first > res) {
                    res = el.first;
                }
            } else {
                for (int x = 0 ; x < 4; x++) {
                    if (posX + pos[x].first >= 0 && posX + pos[x].first < rows && posY + pos[x].second >= 0 && posY + pos[x].second < cols) {
                        if (!visited.contains({posX + pos[x].first, posY + pos[x].second})) {
                            queue.push({el.first + map[{posX + pos[x].first, posY + pos[x].second}], {posX + pos[x].first, posY + pos[x].second}});
                        }
                    }
                }
                visited.insert({posX, posY});
            }
        }
        return res;
    }
};

int main() {
    int rows = 0;
    int cols = 0;
    std::cin >> rows;
    std::cin >> cols;
    //std::cout << rows << " " << cols << std::endl;
    std::map<std::pair<int, int>, int> map1;
    int tmp;
    int sum = 0;
    for (int x = 0; x<rows; x++) {
        for (int y = 0; y<cols; y++) {
            std::cin >> tmp;
            sum += tmp;
            map1.insert({{x, y}, tmp});
        }
    }
    if (rows%2 == 1 || cols%2==1) {
        std::cout << sum << std::endl;
    } else {
        Hamster hamster(rows, cols, map1);
        std::cout << hamster.bfs() << std::endl;
    }
    return 0;
}