using System;

public class Program

{

    public static void Main()

    {

        var arr = new string[]

        {

            "hero_1",

            "hero_2",

            "hero_3",

            "image_1",

            "image_2",

            "image_3",

            "king_1",

            "king_2",

            "king_3"

        };

        var index = -Array.BinarySearch(arr, "king_");

        Console.WriteLine(index);

    }

}

​

​