How to declare in public in all the application?

Hello,
I do not know how to declare a public variable, for example I would like to declare the search for a file and keep for all my application the same value.
Here is my code below, how to always have the name (DBpath).
Thank you in advance.

<pre>          // search the disks if the folder exists
                        string[] drives = Directory.GetLogicalDrives().Where(d => Directory.Exists(Path.Combine(d, "Dossier1"))).ToArray();
                        string Résult = string.Join(", ", drives);


                        if (Résult != "")
                        {
    
                            if (Directory.Exists(Résult + @"Dossier1\"))
                            {

                                if (Directory.Exists(Résult + @"Dossier1\Dossier2"))
                                {

                                    if (File.Exists(Résult + @"Dossier1\Dossier2\BDD_SQLite.db3"))
                                    {
  
                                        string DBpath = Résult + @"Dossier1\Dossier2\BDD_SQLite.db3";


                                    }
                                }
                            }
                        }