open System.IO

let rec getFiles(path:string, maxDepth:int) = seq {
  yield! Directory.EnumerateFiles(path)
  if maxDepth > 0 then
    for subPath in Directory.EnumerateDirectories(path) do
      yield! getFiles(subPath, maxDepth - 1)
}

getFiles("C:\\Projects", 3).Count().Dump()