I had to create the plain text input file in iCloud with my Mac then insert it (Big +, third option) in the iPad’s Swift Playground. Need a text app that will save to Files for a complete iPad solution. Also, a Swift Playground bug reverted my final solution to the code from my first few minutes, losing my code. That was frustrating...

Anyway, a complete Swift Playground on iPad solution:

   import UIKit

   let path = Bundle.main.url(forResource: "input01", withExtension: "txt")
   var text = try String(contentsOf: path!, encoding: .utf8)

   let massList:[Int] = text.components(separatedBy: .whitespacesAndNewlines).compactMap({Int($0)})

   let z1 = massList.map({$0 / 3 - 2}).reduce(0, +)
   print("\(z1)")

You can option+tap a link in Safari to download to Files. Hold down the command key to see available shortcuts.