let n = 10

let rec func (list : string list) (myList: string list) =
    match list with
    | head :: tail -> if (hd myList).Length + head.Length + 1 <= n
                          then func tail (head :: myList)
                      else func tail (head :: (myList |> List.rev |> List.reduce (+)))
    | [] -> myList |> List.rev