#include <iostream>
#include <math.h>
using namespace std;
 
int chess[102][102];
int r, c;
void read ()
{
	cin>>r>>c;
	for (int i=1; i<=r; i++)
	{
		for (int j=1; j<=c; j++)
		{
			cin>>chess[i][j];
		}
	}
}
 
int sumM [102][102];
int x_xq[] = {-1, -2, +1, +2};
int y_xq[] = {-2, -1, -2, -1};
void find_M ()
{
	for (int i=1; i<=r; i++)
	{
		for (int j=1; j<=c; j++)
		{
			int tmp = chess[i][j];
			for (int k=0; k<4; k++)
			{
				int Y = i+y_xq[k];
				int X = j+x_xq[k];
				if (Y>=1 && Y<=r && X>=1 && X<=c)
				{
					tmp = max (tmp, chess[i][j]+sumM[Y][X]);
				}
			}
			sumM[i][j]=tmp;
		}
	}
}
 
int main ()
{
	read ();
	find_M ();
	int Max = 0;
	for (int i=1; i<=r; i++)
	{
		for (int j=1; j<=c; j++)
		{
			Max = max (Max, sumM[i][j]);
		}
	}
	cout<<Max;
	return 0;
}