n = int(input())
A = list(map(int, input().split()))

count = sum(A[::2]) - sum(A[1::2])
ans = count
for i in range(n - 1, -1, -1):
    count -= A[i * 2] * 2
    count += A[i * 2 + 1] * 2
    ans = max(ans, count)
print(ans)