class Program
    {
        static void Main(string[] args)
        {
            string[] coinMoney = Console.ReadLine().Split(' ');
            if (int.Parse(coinMoney[1])/100 < int.Parse(coinMoney[0]))
            {
                Console.WriteLine("can't exchange");
            }
            else
            {
                if ((int.Parse(coinMoney[1]) % 500 / 100) >= int.Parse(coinMoney[0]) && int.Parse(coinMoney[0])  <  5)
                {
                    Console.WriteLine("no exchange");
                }else
                {
                    int remaining = int.Parse(coinMoney[1]) - (int.Parse(coinMoney[0]) * 100);
                    Console.WriteLine(int.Parse(coinMoney[0]) +  (remaining %500/100));
                }
            }
        }
    }