using System;

using System.Globalization;     

​

public class Program

{

    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);

    }

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var date = DateTime.Parse("2024-01-01");

        Console.WriteLine(GetIso8601WeekOfYear(date));

        date = DateTime.Parse("2024-01-07");

        Console.WriteLine(GetIso8601WeekOfYear(date));

        date = DateTime.Parse("2024-01-08");

        Console.WriteLine(GetIso8601WeekOfYear(date));

        date = DateTime.Parse("2024-01-14");

        Console.WriteLine(GetIso8601WeekOfYear(date));

        date = DateTime.Parse("2024-01-15");

        Console.WriteLine(GetIso8601WeekOfYear(date));

    }

}