/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		String email = "any_email@provider.whatever"; 
		String masked = email.replaceAll("(?<=^.|@.)(?<toreplace>[^@]*?)(?=.@|.$)", "***");
		System.out.println(masked); 
	}
}