using System;

using System.Collections.Generic;

public class Program

{

    Random rnd = new Random();

    Nullable<int>[] temp = new Nullable<int>[1024];

    Nullable<int> FindRandom(List<int> input, Func<int, bool> predicate) {

        if (temp.Length < input.Count) {

            temp = new Nullable<int>[input.Count * 2];

        }

        Array.Clear(temp, 0, input.Count);

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

            var index = rnd.Next(i, input.Count);

            int e;

            if (temp[index] != null) {

                e = temp[index].Value;

            } else {

                e = input[index];

            }

            if (predicate(e)) {

                return e;

            }

            temp[index] = input[i];

        }

        return null;

    }

    public static void Main()

    {

    }

}