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

if N == 1:
    print(V[0])
else:
    dp = [0] * N

    dp[0] = V[0]
    dp[1] = V[1]

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

    print(dp[N-1])