program main
  implicit none
  integer*8::N,keta
  integer*8::num(12)
  integer*8::total,i
  read *,N
  keta = 1

  total = -1
  do i=1,12
     total = total + 26**i
     if(total.ge.N) exit
  end do
  keta = i
  N = N - (total - 26**keta) - 1
  do i=1,keta
     num(i) = MOD(N,26)
     N = N/26
  end do

  do i=keta,1,-1
     write(*,'(a)',advance='no') CHAR(ICHAR('A')+num(i))
  end do
  print *,
end program main