using System;

public class Program

{

    public static void Main()

    {

        int a;

        Console.WriteLine("Enter your marks");

        a = Convert.ToInt32(Console.ReadLine());

        if (a<40)

        {

            Console.WriteLine("Grade F");

            }

                 else if (a<50)

            {

                Console.WriteLine("Grade D");

            }

                           else if (a<60)

                           {

                           Console.WriteLine("Grade C");

                            }

                                     else if (a<70)

                                      {

                                      Console.WriteLine("Grade B");

                                      }

                                                else if (a>=70)

                                                 {

                                                 Console.WriteLine("Grade A");

                                                 }

                                             }

                              }