N = int(input())
A_list = list(map(int, input().split()))

A_sum = sum(A_list)
right = [0]
left = [0]
for i in range(N):
    right.append(right[-1]+A_list[i*2])
    left.append(left[-1]+A_list[-1-(i*2)])

homura = max([left[i]+right[-(i+1)] for i in range(N)])

print(2*homura-A_sum)