using System;

using System.Collections.Generic;

using System.IO;

using System.Linq;

using System.Text.RegularExpressions;

​

public class Test

{

    public static void Main()

    {

        var s = "<a href=\"/url?q=https://www.google.com/&sa=U&ved=0ahUKEwizwPy0yNHSAhXMDpAKHec7DAsQFgh6MA0&usg=AFQjCNEjJILXPMMCNAlz5MN1IIzjpr79tw\">";

        var pattern = @"<a href=""/url\?q=(.*?)&";

        var result = Regex.Match(s, pattern);

        if (result.Success)

            Console.WriteLine(result.Groups[1].Value);

    }

}