program ordinary_beauty
  implicit none
  integer :: n, m, d
  real(8) :: p
  character(64) :: s
  read(*,*) n, m, d
  p = 0.d0
  if (d.eq.0) then
    p = real(m-1,8)/real(n,8)
  else
    p = real(m-1,8)*real(n-d,8)/real(n,8)
  end if
  write(s,'(f32.16)') p
  write(*,'(a)') trim(adjustl(s))
  return
end program ordinary_beauty