N = int(input())

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

A1 = A[::2]
A2 = A[-1::-2]

X = [0]
Y = [0]
for a in A1:
    X += [X[-1] + a]
for a in A2:
    Y += [Y[-1] + a]
print(max([X[i] + Y[N - i] for i in range(N + 1)]) * 2 - sum(A))