using System;

using System.Collections.Generic;

using System.Globalization;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var input = "3e43";

        var val = double.Parse(input, NumberStyles.AllowExponent | NumberStyles.AllowDecimalPoint);

        Console.WriteLine(val);

        Console.WriteLine(val.ToString("N0"));

        Console.WriteLine(val.ToString("f"));

    }

}