using System;

public class Program

{

    public static void Main()

    {

        var input = new DateTime(2021, 03, 26);

        //var newInput = input.AddDays(-1);

        if (input.DayOfWeek == DayOfWeek.Friday)

        {

            input = input.AddDays(-7);

        }

        else 

        {

            while (input.DayOfWeek != DayOfWeek.Friday)

            {

                input = input.AddDays(-1);

            }

        }

        Console.WriteLine(input);

    }

}