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

def solve(N, Vs):
    if N == 1:
        return Vs[0]
    dp = [0] * N
    dp[0] = Vs[0]
    dp[1] = max(Vs[0], Vs[1])
    for i, v in enumerate(Vs[2:], 2):
        dp[i] = max(dp[i-1], dp[i-2] + v)
    return dp[-1]

print(solve(N, Vs))