import sys
def input():
	return sys.stdin.readline()[:-1]
n, m = map(int, input().split())
a = [sum(list(map(int, input().split()))) for _ in range(n)]
INF = 10**15
dp = [[-INF for _ in range(2)] for _ in range(n+1)]
dp[0][0] = 0
for i in range(1, n+1):
	x = a[i-1]
	dp[i][0] = max(dp[i-1][0], dp[i-1][1] - x)
	dp[i][1] = max(dp[i-1][1], dp[i-1][0] + x)
print(max(dp[n]))