dp = [0] * 2 # 最後にたべたものを2で割った余り
dp[1] = -(1 << 60)

N,M = map(int,input().split())
for _ in range(N):
    val = sum(map(int,input().split()))
    new_dp = dp.copy()
    new_dp[0] = max(new_dp[0], dp[1] - val)
    new_dp[1] = max(new_dp[1], dp[0] + val)
    dp = new_dp

print(max(dp))