using System;

public class Program

{

    public static void Main()

    {

        double final_marks=0;

        Console.WriteLine("Enter Student Final Mark:");

        final_marks=Convert.ToDouble(Console.ReadLine());

        if(final_marks>=75){

        Console.WriteLine("Grade:A");

        }else if  (final_marks>=65){

            Console.WriteLine("Grade:B");

        }else if (final_marks>=55){

        Console.WriteLine("Grade:C");

        }else{

            Console.WriteLine("Grade:F");

    }

    }}