import sys, re
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians, gcd
from itertools import accumulate, permutations, combinations, product, groupby, combinations_with_replacement
from operator import itemgetter, mul
from copy import deepcopy
from string import ascii_lowercase, ascii_uppercase, digits
from bisect import bisect, bisect_left
from heapq import heappush, heappop
from functools import reduce
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
def ZIP(n): return zip(*(MAP() for _ in range(n)))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7

N, M = MAP()
A = [sum(LIST()) for _ in range(N)]

dp = [[0]*2 for _ in range(N+1)]

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

print(dp[-1][1])