#include <iostream>
#include <vector>

using namespace std;

void bfs(vector<vector<int>> &input, vector<vector<int>> &visited, int dir, int score, int pos_n, int pos_m, int N, int M);

int ans = 0;

int main() {
    int N, M;
    cin >> N >> M;

    vector<vector<int>> input(N, vector<int>(M, 0));
    //vector<vector<vector<int>>> best(N, vector<vector<int>>(M, vector<int>(4, 0)));
    vector<vector<int>> visited(N, vector<int>(M, 0));

    for (int i = 0; i < N; ++i) {
        for (int j = 0; j < M; ++j) {
            cin >> input[i][j];
        }
    }

    bfs(input, visited, 0, 0, 0, 0, N, M);


    cout << ans << '\n';

    return 0; 
}

void bfs(vector<vector<int>> &input, vector<vector<int>> &visited, int dir, int score, int pos_n, int pos_m, int N, int M) {
    if (pos_n < 0 || pos_n >= N || pos_m < 0 || pos_m >= M) {
        return;
    }

    if (visited[pos_n][pos_m] == 1) {
        return;
    }

    int current_score = score + input[pos_n][pos_m];

    if (pos_n == N - 1 && pos_m == M - 1) {
        ans = max(ans, current_score);
        return;
    }

    visited[pos_n][pos_m] = 1;
    bfs(input, visited, 0, current_score, pos_n+1, pos_m, N, M);
    bfs(input, visited, 1, current_score, pos_n-1, pos_m, N, M);
    bfs(input, visited, 2, current_score, pos_n, pos_m+1, N, M);
    bfs(input, visited, 3, current_score, pos_n, pos_m-1, N, M);
    visited[pos_n][pos_m] = 0;

    return;
}