using System;
using System.Collections.Generic;
using System.Globalization;
using System.Text;
using System.Text.RegularExpressions;
using System.Reflection;
public class MainClass{
public static void Main(){
Regex r = new Regex(@"(^\d+$\n)+", RegexOptions.Multiline);
Console.WriteLine(r.Match("987987\n129821").Value);
}
}