let rec pow x n = 
  if n = 0
  then 1
  else 
    let res = pow x (n/2) in
    if n mod 2 = 0
    then res * res
    else res * res * x

(* purpose: calulate 26^1 + 26^2 + .. + 26^n *)
(* for convenience, sum 0 = 0 *)
(* sum: int -> int *)
let rec sum n =
  if n = 0
  then 0
  else pow 26 n + sum (n-1)

let digit n =
  let rec iter i =
    if n < sum i
    then i
    else iter (i+1)
  in iter 1

(* purpose : encode n into k-digits alphabet *)
let encode n k =
  let rec iter num i str =
    if i = k+1
    then str
    else 
      let add = Char.chr (Char.code 'a' + (num mod 26)) in
      let new_str = String.make 1 add ^ str in
      iter (num/26) (i+1) new_str
  in iter n 1 ""

let () = Scanf.scanf "%d" @@ fun n ->
  let n = n-1 in
  let k = digit n in
  let n = n - sum (k-1) in
  let ans = encode n k in
  Printf.printf "%s\n" ans