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

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 >> m >> n;
    std::vector<std::vector<int>> map(n);

    for (int i = 0; i < n; ++i) {
        map[i].resize(m);
        for (int j = 0; j < m; ++j)
            std::cin >> map[i][j];
    }

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

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

    return 0;
}