N, M = map(int, input().split())
A = []
for i in range(N):
    A.append(sum(map(int, input().split())))

inf = 10 ** 18 
dp = [[-inf] * 2 for i in range(N + 1)]
dp[0][0] = 0
for i in range(N):
    for j in range(2):
        dp[i + 1][j] = max(dp[i + 1][j], dp[i][j])
        dp[i + 1][1 - j] = max(dp[i + 1][1 - j], dp[i][j] + A[i] * (-1) ** j)
print(max(dp[-1]))