using System;

public class Program

{

    public static void Main()

    {

        int month ;

           Console.Write("please enter month:");

            month = int.Parse(Console.ReadLine());

            if (month < 1 || month > 12)

                Console.WriteLine("Error!");

            else

            {

                if ((month == 1) || (month == 3) || (month == 5) || (month == 7) || (month == 8) || (month == 12))

                    Console.WriteLine("month = 31");

​

                else if ((month == 2))

                    Console.WriteLine("month = 28");

                else

                    Console.WriteLine("month = 30");

​

​

            }

    }

}