using System;
using System.Text.RegularExpressions;
public class Test
{
	public static void Main()
	{
    string nameString = @"C:\Users\Documents\Development\testing\11.0.25.10\W_11052_0_X.pts";
    string pathPrefix = Regex.Match(nameString, @"^(.*[\\])").Groups[1].Value;
    Console.WriteLine(pathPrefix);
	}
}