from collections import *
from itertools import *
from functools import *
from heapq import *
import math,sys
input = sys.stdin.readline

N,M = map(int,input().split())
A = [list(map(int,input().split())) for _ in range(N)]
C = [sum(A[i]) for i in range(N)]

dp = [[0]*N for _ in range(2)]
dp[1][0] = C[0]
for i in range(N-1):
    
    
    dp[0][i+1] = max(dp[0][i],-C[i+1]+dp[1][i])
    dp[1][i+1] = max(dp[1][i],C[i+1]+dp[0][i])
    
print(max(dp[0][-1],dp[1][-1]))