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

yummy = [0] * N
yummy[0] = V[0]

if N < 2:
    print(yummy[0])
else:
    yummy[1] = max(V[0], V[1])
    for i in range(2, N):
        yummy[i] = max(yummy[i-2] + V[i], yummy[i-1], yummy[i-2])
    print(yummy[N-1])