using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string input = "itsarun.sunny@yahoo.com";

        string pattern = @"(?<=[\w]{1})[\w-\._\+%]*(?=[\w]{1}@)";

        string maskedEmail = Regex.Replace(input, pattern, m => new string('*', m.Length));

        System.Console.WriteLine(maskedEmail);

    }

}