from sys import stdin

N,M = map(int,stdin.readline().split())

A = []

for i in range(N):

    a = sum( list(map(int,stdin.readline().split())) )
    A.append(a)

dp = [0,0]

for i in range(N):

    ndp = [float("-inf"),float("-inf")]
    ndp[0] = max(dp[0],dp[1]-A[i])
    ndp[1] = max(dp[1],dp[0]+A[i])

    dp = ndp

print (max(dp))