N = int(input())

V = [int(i) for i in input().split()]

if N == 1:
    print(V[0])
    exit(0)

if N == 2:
    print(max(V[0], V[1]))
    exit(0)

S = [V[0], V[1], V[2]]

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

print(max(S[N - 1], S[N - 2]))