using System;

public class Program

{

    public static void Main()

    {

​

        int[] A = {1,2,3,4,5};

        int X = 5;

    //public int solution(int[] A, int X) 

        int N = A.Length;

        if (N == 0) {

            Console.WriteLine(-1);

            //return (-1);

        }

        int l = 0;

        int r = N - 1;

        while (l < r) {

            int m = (l + r) / 2;

            if (A[m] > X) {

                r = m - 1;

            } else {

                l = m;

            }

        }

        if (A[l] == X) {

            Console.WriteLine(1);

            //return l;

        }

        //return -1;

        Console.WriteLine(-1);

    }

}