using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Please enter your score:");

        int iScore =0;

        string strScore = Console.ReadLine();

        bool IsValidNumber = Int32.TryParse(strScore, out iScore);

        if (IsValidNumber == false)

        {

            Console.WriteLine("Please enter a valid number!");

            return;

        }

        else

        {

            Console.WriteLine("Valid whole number");

        }

        if (!(iScore>=0 && iScore<=100))

        {

            Console.WriteLine("Please enter a valid score");

            return;

        }

        else

        {

            Console.WriteLine("Score is between 0 and 100");

        }   

        if(iScore>=90)

            Console.WriteLine("You get A");

        else if(iScore>=80 && iScore<=89)

            Console.WriteLine("You get B");

        else if(iScore>=70 && iScore<=79)

            Console.WriteLine("You get C");

        else if(iScore>=60 && iScore<=69)

            Console.WriteLine("You get D");

        else

            Console.WriteLine("You get F");

    }

}