N=int(input())
V=list(map(int, input().split()))
if N == 1:
    print(V[0])
    exit()
elif N == 2:
    print(max(V[0],V[1]))
    exit()
elif N == 3:
    print(max(V[0]+V[2], V[1]))
    exit()

dp=[V[0],V[1],V[0]+V[2]]
for i in range(3,N):
    dp.append(max(dp[-1], dp[-2]+V[i], dp[-3]+V[i]))

print(dp[-1])