using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

         // Seriously cheat.  If its Monday, Tuesday or Wednesday, then it'll 

    // be the same week# as whatever Thursday, Friday or Saturday are,

    // and we always get those right

        DateTime dt = DateTime.Parse("2022/01/01");

        Console.WriteLine("Week: "+GetIso8601WeekOfYear(dt));

    }

    public static int GetIso8601WeekOfYear(DateTime time)

{   

    DayOfWeek day = CultureInfo.InvariantCulture.Calendar.GetDayOfWeek(time);

    if (day >= DayOfWeek.Monday && day <= DayOfWeek.Wednesday)

    {

        time = time.AddDays(3);

    }

​

    // Return the week of our adjusted day

    return CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);

} 

}