using System;

​

public class dttimeex55

{

    public static void Main()

    {

        var DatetimeNow = new DateTime(2021, 4, 30);

        int daysToAdd = System.DateTime.DaysInMonth(DatetimeNow.Year, DatetimeNow.Month) - DatetimeNow.Day;

        Console.Write("days left : "  + daysToAdd.ToString());

    }

}