using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		string exp1 = @"\d+G-\w{3}";
		string s = "CN=314G-VK1,OU=Grupper,OU=314,OU=Skole,OU=03Skien,DC=login,DC=sk-asp,DC=no";
		string z = Regex.Match(s, exp1)?.Value;
		Console.WriteLine(z);
	}
}