using System;

public class Program

{

    public static void Main()

    {

        string xyz = "http://localhost:81/LogOn.aspx?LogOff=true";

        int index = xyz.IndexOf("Logon",System.StringComparison.OrdinalIgnoreCase);

        Console.WriteLine(index);

        xyz = xyz.Substring(0,index);

        Console.WriteLine(xyz);

    }

}