using System;
using System.Linq;
using System.Xml;
using System.Collections.Specialized;
using System.Web;
using System.Text;
using System.Net;
using System.Collections.Generic;
public class C {
public static void Main() {
var r1 = new Y().Do("b");
var r2 = r1.ToList();
foreach(var r in r1)
{
}
/*
foreach(var r in r2)
}*/
public class Y
public IEnumerable<string> Do(string s)
yield return s;
Console.WriteLine("input " + s + " found");
Console.WriteLine("C");