using System;

using System.Collections.Generic;

using System.Collections;

public class Program

{

    public static void Main(string[] args)

        {

            var a = new List<int> { 1, 9, 5, 100, 22, 18, 5 };

            RemoveOdd(a);

            Console.WriteLine(string.Join(",", a));

        }

        private static void RemoveOdd(List<int> a)

        {

            RemoveRecursionOdd(a);

        }

        private static List<int> RemoveRecursionOdd(List<int> a)

        {

            if (a.Count == 0)

                return a;

            foreach (var i in a)

            {

                if (i == 100) {

                    Console.WriteLine("100!");

                }

                if (i % 2 != 0)

                {

                    a.Remove(i);

                    return RemoveRecursionOdd(a);

                }

            }

            return a;

        }

​

}