using System;

public class Program

{

    public static void Main()

    {

        //1. Read input from user

        Console.WriteLine("Please enter a whole number");

        string strInput = Console.ReadLine();

        //2. Validate this input (check whether it is a valid whole number)

        int Score;

        bool IsValidNumber = Int32.TryParse(strInput, out Score);

        if(IsValidNumber == false)

        {

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

            return;

        }

        Console.WriteLine("===============================");

        //3. Show the following information 

        // Input: >= 90, show message "You get A".

        // Input: 80 ~ 90, show message "You get B".

        // Input: 70 ~ 80, show message "You get C".

        // Input: 60 ~ 70, show message "You get D".

        // Input: <= 60, show message "You get F".

        if (Score >= 90)

        {

            Console.WriteLine("You get A");

            Console.WriteLine("Please tell me your major");

            string strInput2 = Console.ReadLine();

            if (strInput2 == "IS")

            {

                Console.WriteLine("Congrats!");

            }

        }

        else if (Score >= 80)

        {

            Console.WriteLine("You get B");

        }

        else if (Score >= 70)

        {

            Console.WriteLine("You get C");

        }

        else if (Score >= 60)

        {

            Console.WriteLine("You get D");

        }   

        else

        {

            Console.WriteLine("You get F");

        }

        //4. For individual's score greater than 90, check his/her major

        //Show "Congratulations! You are one of the best students in IS" if the major is IS

    }

}