import sys
readline = sys.stdin.readline

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

A = [sum(list(map(int, readline().split()))) for _ in range(N)]

INF = 10**18

even = 0
odd = -INF

for a in A:
    even, odd = max(even, odd - a), max(odd, even+a)

print(max(even, odd))