using System;

public class Program

{

    public static void Main()

    {

        Console.Write("Enter a letter grade: ");

        string grade = Console.ReadLine();

        bool grades;

        if(bool.TryParse(grade,out grades)){

            switch (grade) 

            {           

              case "A":

                Console.WriteLine("January: 31 days");

                break;

              case "B":

                Console.WriteLine("February: 28 days");

                break;

              case "C":

                Console.WriteLine("March: 31 days");

                break;

              case "D":

                Console.WriteLine("April: 30 days");

                break;

              case "F":

                Console.WriteLine("May: 31 days");

                break;

                }

        } else{

            Console.Write("Not valid input");

    }

}

}