Substring outofindex

Question

I wrote a code for which

if 23E+20 is the input then output should be 230000000(20 zeros)

if 4.456E-14 is the input then 4.456000(14 zeros) should be the output

But its not working properly. Please let me know where I did error. Thank You.

using System;

class test

{

public static void Main()

{

Console.WriteLine("Enter double");

      String ext =Console.ReadLine();



           if(ext.IndexOf("E")!=-1)
        {
           int i=ext.IndexOf("E");

          ext = ext.Substring(0, i);

          for (int j = 0; j < int.Parse(ext.Substring(i + 1, ext.Length - (i + 1))); j++)

          ext = ext + "0";         

          Console.WriteLine(ext);



      }

}