using System;

public class Program

{

    public static void Main()

    {

        var date1 = new DateTime(2021, 7, 1);

        Console.WriteLine(date1.AddMonths(-1).ToString("dd.MM.yyyy"));

        Console.WriteLine(date1.ToString("dd.MM.yyyy"));

        var date2 = new DateTime(2021, 1, 1);

        Console.WriteLine(date2.AddMonths(-1).ToString("dd.MM.yyyy"));

        var date3 = new DateTime(2020, 3, 28);

        Console.WriteLine(date3.AddMonths(-1).ToString("dd.MM.yyyy"));

    }

}