#回転ずし

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

total = list(0 for i in range(N))

if N == 1:
    total[0] = V[0]
elif N == 2:
    total[1] = max(V)
else:
    total[0] = V[0]
    total[1] = V[1]
    if N == 3:
        total[2] = max(V[0] + V[2] , V[1])
    else:
        for i in range(2 , N):
            total[i] = max(total[i - 2] + V[i] , total[i - 3] + V[i] , total[i - 1])

print(total[N-1])