using System;

public class Program

{

    public static void Main()

    {

        string emailSubject = "Invoice for order BOS-12345 is here";

        //get the second character because 0 is the first one.

        Console.WriteLine(emailSubject.IndexOf("BOS"));

        int orderNumberPosition = emailSubject.IndexOf("BOS");

        Console.WriteLine(emailSubject.Substring(orderNumberPosition, 9));

    }

}