import sys
import numpy as np
readline = sys.stdin.readline

n, m = map(int, readline().split())
a = b = 0

for i in range(n):
    umai = np.sum(np.array(readline().split(),
                           dtype=np.int64), dtype=np.int64)
    a, b = max(b - umai, a), max(a + umai, b)
print(max(a, b))