using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
	    string txt = "e1e2e3";
        Regex digits = new Regex(@"\d");
        Random rand = new Random();
        txt = digits.Replace(txt, match => rand.Next(0, 9).ToString());
        Console.WriteLine(txt);
	}
}