#include <iostream>
#include <vector>

using namespace std;

static vector<vector<int>> memo;
static vector<vector<bool>> visited;

void rec(vector<vector<int>>& pole, int larvy, int x, int y, int n, int m)
{
	if (x >= n || x < 0 || y >= m || y < 0)
		return;
	if (visited[x][y])
		return;
	int larvyteraz = larvy + pole[x][y];
	if (x == n - 1 && y == m - 1)
	{
		if (larvyteraz > memo[x][y])
			memo[x][y] = larvyteraz;
		return;
	}
	if (larvyteraz > memo[x][y])
	{
		memo[x][y] = larvyteraz;
	}
	visited[x][y] = true;
	rec(pole, larvyteraz, x - 1, y, n, m);
	rec(pole, larvyteraz, x, y + 1, n, m);
	rec(pole, larvyteraz, x + 1, y, n, m);
	rec(pole, larvyteraz, x, y - 1, n, m);
	visited[x][y] = false;
	return;
}

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];
		}
	}
	visited = vector<vector<bool>>(n, vector<bool>(m));
	memo = vector<vector<int>>(n, vector<int>(m));
	rec(pole, 0, 0, 0, n, m);
	cout << memo[n - 1][m - 1];
	return 0;
}