#!/usr/bin/perl

use strict;
use warnings;
use Memoize;
memoize 'fibo';

my $val = shift;
printf "%.12f\n", fibo($val+1)/fibo($val);

sub fibo {
	my $n = shift;
	return $n if ($n < 2);
	return fibo ($n-1) + fibo ($n-2);
}