n = int(input())
V = list(map(int,input().split()))

if n == 1 :
    print(V[0])
elif n == 2:
    print(max(V))
else:
    dp = [0] * n
    dp[0] = V[0]
    dp[1] = max(V[0], V[1])

    for i, v in enumerate(V[2:], 2):
        dp[i] = max(dp[i-1], dp[i-2] + v)

    print(dp[n-1])