let nameChars n =
    let rec nameCharsRev lst n =
        let n = n - 1L
        match n / 26L, n % 26L with
        | 0L, rem -> rem :: lst
        | q, rem -> nameCharsRev (rem :: lst) q

    nameCharsRev [] n |> List.rev

stdin.ReadLine()
|> int64
|> nameChars
|> List.toArray
|> Array.rev
|> Array.map (fun num -> char (num + 97L))
|> System.String.Concat
|> printfn "%s"
