using System;

using System.Collections;

​

public class Program

{

    public static object GetRandomNumber(IEnumerator it) {

        var i = 0;

        object res = null;

        while (it.MoveNext()){

            var k = new Random(Environment.TickCount).Next(i);

            ++i;

            if (k == 0){ 

                res = it.Current;

            }

        }

        return res;

    }

    public static void Main()

    {

        Console.WriteLine(GetRandomNumber(new int[]{1,2,3,4,5,6,7}.GetEnumerator()));

    }

}