import sys
input = sys.stdin.readline
from collections import *

N, M = map(int, input().split())
A = [sum(list(map(int, input().split()))) for _ in range(N)]
dp = [[0]*2 for _ in range(N+1)]

for i in range(N):
    dp[i+1][0] = max(dp[i][0], dp[i][1]-A[i])
    dp[i+1][1] = max(dp[i][1], dp[i][0]+A[i])

print(max(dp[N]))