using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        var regex = new Regex(@"value=""([\d,]+)""");

        var match = regex.Match("<input style=\"width: 2.3em;\" id=\"nacional\" value=\"3,48\" type=\"text\">");

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

    }

}