import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

n,m = map(int,readline().split())
a = [ sum(map(int, i.split())) for i in readlines()]

dp = [0] * 2
dp[0] = -1 * 10**15

for ai in a:
    dp[0] = max(dp[0],dp[1]+ai)
    dp[1] = max(dp[1],dp[0]-ai)

print(max(dp))