import sys
input = sys.stdin.buffer.readline
sys.setrecursionlimit(10 ** 7)

N, M = map(int, input().split())
e = 0
o = 0
for _ in range(N):
    A = sum(map(int, input().split()))
    e, o = max(e, o - A), max(o, e + A)

print(max(e, o))