#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <iomanip>
using namespace std;
int main(void){
	int i;
	double a, b;
	int n;
	cin >> n;
	double Fn;
	double q=1,w=1;
	for(i=0;i<n;i++){
		q = q*((1+sqrt(5))/2);
		w = w*((1-sqrt(5))/2);
	}
	Fn = (a-b)/sqrt(5);
	printf("%.2lf",Fn);
    return 0;
}