using System;

using System.Text;

using System.Text.RegularExpressions;                   

public class Program

{

    public static void Main()

    {

        string input = "CASA_ARAGON_22/001710860654/Logical Upstream Channel 4/10.0/0";

        Console.WriteLine(Regex.Match(input,@"[^/]+/[^/]+/[^/]+").input.Substring(input.Length - 1, 1));

        // or

        Console.WriteLine(input.Substring(input.Length - 1, 1));

    }

}