import math.BigInt
object Main extends App {
  val in = new java.util.Scanner(System.in)

  def exec(n: BigInt, l: List[Char]): String = {
    if (n == 0) l.mkString
    else {
      val rem = (n - 1).mod(26)
      exec((n - rem) / 26, ('a' + rem).toChar :: l)
    }
  }

  println(exec(BigInt(in.next), Nil))
}