using System;

public class Program

{

    public static void Main()

    {

        var stringOf55Characters= "ROB/123456789123456789123456789123456789123456789123456789123456789LOL";

        var x = stringOf55Characters.Length < 50 ? 0 : stringOf55Characters.Length - 50;

        var string3 = stringOf55Characters.Substring(x, 50);

        Console.WriteLine(string3); 

    }

}