N = int(raw_input())

data = map(int, raw_input().split())

dp = [0] * N

if N == 1:
    print data[0]
else:
    dp[0] = data[0]
    dp[1] = data[1]
    for i in xrange(2, N):
        dp[i] = max(dp[i - 2], dp[i - 3]) + data[i]

    print max(dp[N - 1], dp[N - 2])