using System;

public class Program

{

    public static void Main()

    {

        var a = new []{ 1, 5, 7, 2, 3, 10 };

        Array.Sort(a);

        Console.WriteLine(binarySearch(a, 4));

    }

    public static int binarySearch<T>(T[] a, T x)

    {

        var result = Array.BinarySearch<T>(a, x);

        return result >= 0 ? result : -1;

    }

}