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