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

if n == 0:
    print(0)
else:
    dp = [0] * (n + 1)
    dp[1] = v[0]
    for i in range(2, n + 1):
        dp[i] = max(dp[i-1], dp[i-2] + v[i-1])
    print(dp[n])