using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var folders = new List<(int, string, int?)>{

            (1, "one", null),

            (2, "two", 1),

            (3, "three", 2),

            (4, "four", 3)

        };

        int leafFolder = 4;

        var orderedFolders = GetFolderPath(leafFolder, folders);

        Console.WriteLine(string.Join('/',orderedFolders));

    }

    private static IList<string> GetFolderPath(int? folder, IList<(int id,string name,int? parent)> folders){

        if(folder == null) return new List<string>();

        var f = folders.Single(f=>f.id == folder);

        return GetFolderPath(f.parent, folders).Concat(new List<string>{f.name}).ToList();

    }

}