using System;

using System.Collections;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        ArrayList list = new ArrayList(new object[] { "a","a","a","a","a"});

        for(int i = 0; i < list.Count; i++)

            {

                if(list[i] == "a")

                {

                    list.RemoveAt(i);

                    list.Insert(i, 1);

                    break;

                }

            }

        for(int i = 0; i < list.Count; i++){

            Console.WriteLine(list[i]);

        }

        for(int i = 0; i < list.Count; i++)

            {

                if(list[i] == "a")

                {

                    list.RemoveAt(i);

                    list.Insert(i, 1);

                    break;

                }

            }

        for(int i = 0; i < list.Count; i++){

            Console.WriteLine(list[i]);

        }   

    }

}