using System;

class A
{
    public void markpro()
    {
        Console.WriteLine("please input a mark");
        while(true)
        {
            int mark=int.Parse(Console.ReadLine());
            mark=mark/10;
            switch(mark)
            {
                case 10:
                    Console.WriteLine("A");
                    break;
                case 9:
                    Console.WriteLine("A");
                    break;
                case 8:
                    Console.WriteLine("B");
                    break;
                case 7:
                    Console.WriteLine("C");
                    break;
                case 6:
                    Console.WriteLine("D");
                    break;
                default:
                    Console.WriteLine("fail");
                    break;
            }
        }
    }
}

class B
{
    static void Main()
    {
        A a=new A();
        a.markpro();
    }
}