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

    dp = [0 for i in range(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])


if __name__ == '__main__':
    main()