#include <algorithm>
#include <limits>
#include <cstdio>
#include <iostream>

using namespace std;
using u64 = long long;

int n, m;
int hamster[1001][1001];
bool visited[1001][1001]{};

struct result {
    int sum;
    bool success;
};

result dfs(int x, int y) {
    if (x < 0 || y < 0 || x >= n || y >= m) {
        return { 0, false };
    }

    if (visited[x][y]) {
        return { 0, false };
    }

    if (x == n - 1 && y == n - 1) {
        return { hamster[x][y], true };
    }

    int best = 0;
    bool success = false;
    visited[x][y] = true;

    result res = dfs(x + 1, y);

    if (res.success) {
        best = std::max(best, res.sum);
        success = true;
    }

    res = dfs(x, y + 1);

    if (res.success) {
        best = std::max(best, res.sum);
        success = true;
    }

    res = dfs(x - 1, y);

    if (res.success) {
        best = std::max(best, res.sum);
        success = true;
    }

    res = dfs(x, y - 1);

    if (res.success) {
        best = std::max(best, res.sum);
        success = true;
    }

    visited[x][y] = false;
    return { best + hamster[x][y], success };
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    cin >> n >> m;

    u64 sum = 0;

    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) {
            cin >> hamster[i][j];
            sum += hamster[i][j];
        }
    }

    if (n % 2 == 1 || m % 2 == 1) {
        printf("%llu\n", sum);
        return 0;
    }

    result res = dfs(0, 0);
    printf("%d\n", res.sum);
}