n, m = map(int, input().split())
A = [list(map(int, input().split())) for _ in range(n)]
S = [sum(a) for a in A]
#print(S)

INF = 10**18
# dp[i][j]: jはこれまでのカウントのmod2
dp = [[-INF]*2 for _ in range(n+1)]
dp[0][0] = 0
for i in range(n):
    dp[i+1][0] = dp[i][0]
    dp[i+1][1] = dp[i][1]
    dp[i+1][1] = max(dp[i+1][1], dp[i][0]+S[i])
    dp[i+1][0] = max(dp[i+1][0], dp[i][1]-S[i])
print(max(dp[-1]))