#include <map>
#include <set>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;
int cow[200010];
int dp[200010];
int col[200010];
int dp2[200010];

int main()
{
	int n, m;
	while (~scanf("%d%d", &n, &m))
	{
		memset (dp2, 0, sizeof(dp2));
		for (int i = 1; i <= n; ++i)
		{
			memset (dp, 0, sizeof(dp));
			for (int j = 1; j <= m; ++j)
			{
				scanf("%d", &cow[j]);
			}
			dp[1] = cow[1];
			for (int j = 2; j <= m; ++j)
			{
				dp[j] = max(dp[j - 1], dp[j - 2] + cow[j]);
			}
			col[i] = dp[m];
		}
		dp2[1] = col[1];
		for (int i = 2; i <= n; ++i)
		{
			dp2[i] = max(dp2[i - 1], dp2[i - 2] + col[i]);
		}
		printf("%d\n", dp2[n]);
	}
	return 0;
}