n = int(input())
a = list(map(int, input().split()))
t = 0
for i in range(n - 1, -1, -1):
    t += a[i * 2 + 1] - a[i * 2]
ans = t
for i in range(n):
    t += (a[i * 2] - a[i * 2 + 1]) * 2
    ans = max(ans, t)
print(ans)