using System;

public class Program

{

    public static void Main()

    {

        for(int month=1;month<13;month++)

        {

            DateTime current = new DateTime(2020,month,1);

            Console.WriteLine("At current {0:yyyyMMdd} nextMonth {1:yyyyMMdd}",current,endMonth(current));

        }

    }

    public static DateTime endMonth(DateTime E71)

    {

        var nextMonth =EDATE(E71,1); 

        return MONTH(nextMonth)<7?DATE(YEAR(nextMonth),6,1):DATE(YEAR(nextMonth),12,1);

    }

    public static DateTime EDATE(DateTime date,int monthIncrement)

    {

        return date.AddMonths(monthIncrement);

    }

    public static int MONTH(DateTime date)

    {

        return date.Month;  

    }

    public static int YEAR(DateTime date)

    {

        return date.Year;   

    }

    public static DateTime DATE(int year,int month,int day)

    {

        return new DateTime(year,month,day);

    }

}