using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

​

    public static void Main()

    {

        string test = "Jack Nelsson";

        var firstname = test != null ? test.Substring(0, test.LastIndexOf(" ")) : "";

        var lastname =  test != null ? test.Split(' ').Last() : "";

        Console.WriteLine(firstname);

        Console.WriteLine(lastname);

    }

}