N, *V = map(int, open(0).read().split())

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

print(dp[N - 1])