title: Get week from selected monthcalendar-date
body: <p>I need a solution to calculate the week from the selected date. (in monthcalendar)<br>
  I tried:</p>
  
  <pre><code>DateTime dt1 = new DateTime(monthCalendar1.SelectionStart.Year, 
                              monthCalendar1.SelectionStart.Month, 
                              monthCalendar1.SelectionStart.Day);
  
  DateTime dt2 = new DateTime(monthCalendar1.SelectionStart.Year, 
                              1, 
                              1);
  
  System.TimeSpan varTime = dt1 - dt2;
  int weeks = (varTime.Days / 7) + 1;
  </code></pre>
  
  <p>But start and enddays of a weeks are not correct and in some years I got 53 weeks?<br>
  what is the best way to solve this?</p>