using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var link = "https://m.facebook.com/pages/creation_flow/?step=contact_info&page_id=108019410876807&draft_id=1567676760072255";

         Regex regex = new Regex(@"page_id\=[0-9]*");

         Match match = regex.Match(link);

        if (match.Success)

        {

            var fb_id = match.Value.Replace("page_id=", "");

            Console.WriteLine(fb_id);

        }

    }

}