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");

    }

}