using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Enter Score: ");

        int score = Convert.ToInt32(Console.ReadLine());

        if(score >= 0 && score < 50)

        {

            Console.WriteLine("Grade F");

        }

        else if(score >= 0 && score < 60)

        {

            Console.WriteLine("Grade D");

        }

        else if(score >= 0 && score < 70)

        {

            Console.WriteLine("Grade C");

        }

        else if(score >= 0 && score < 80)

        {

            Console.WriteLine("Grade B");

        }

        else if(score >= 0 && score <= 100)

        {

            Console.WriteLine("Grade A");

        }

        else 

        {

            Console.WriteLine("Error");

        }

    }

}