#include <iostream>
#include <vector>

using namespace std;

int rec(vector<vector<int>>& pole, vector<vector<bool>> visited, int larvy, int x, int y, int n, int m)
{
	if (x >= n || x < 0 || y >= m || y < 0)
		return larvy;
	if (visited[x][y])
		return larvy;
	if (x == n - 1 && y == m - 1)
		return pole[x][y] + larvy;
	int larvyteraz = larvy + pole[x][y];
	visited[x][y] = true;
	int hore = rec(pole, visited, larvyteraz, x + 1, y, n, m);
	int dole = rec(pole, visited, larvyteraz, x - 1, y, n, m);
	int doprava = rec(pole, visited, larvyteraz, x, y + 1, n, m);
	int dolava = rec(pole, visited, larvyteraz, x, y - 1, n, m);
	vector<int> p = { hore, dole, doprava, dolava };
	int max = -1;
	for (int i = 0; i < 4; i++)
	{
		if (p[i] > max)
			max = p[i];
	}
	return max;
}

int main()
{
	int n, m;
	cin >> n >> m;
	vector<vector<int>> pole = vector<vector<int>>(n,vector<int>(m));
	for (int i = 0; i < n; i++)
	{
		for (int j = 0; j < m; j++)
		{
			cin >> pole[i][j];
		}
	}
	vector<vector<bool>> vis = vector<vector<bool>>(n, vector<bool>(m));
	cout << rec(pole, vis, 0, 0, 0, n, m);
	return 0;
}