Retrieve system uptime using C#

I know question is both old and solved, but the esiest solution I can tink of is just using the Enviroment.TickCount property, which returns the number of millisecounds since the system started:

System.DateTime SystemStartTime = DateAndTime.Now.AddMilliseconds(-Environment.TickCount);
System.DateTime Uptime = DateAndTime.Now - SystemStartTime;

This solition is a lot faster than the accepted answare.