// yukicoder My Practice
// author: Leonardone @ NEETSDKASU

let n = int64(System.Console.ReadLine())

let al = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"

let rec f n r =
    if n < 0L then
        r
    else
        let i = string al.[int(n % 26L)]
        f (n / 26L - 1L) (i + r)

printf "%s" <| f n "\n"