program main
  implicit none
  integer*8::N,i
  integer*8,allocatable::pat(:)
  read *,N
  allocate(pat(-1:N))

  pat(-1) = 0
  pat(0)  = 1
  do i=1,N
     pat(i) = pat(i-1) + pat(i-2)
  end do
  print '(i0)',pat(N)
end program main