#include <iostream>
#include <stdlib.h>
#include <bitset>
#include <iomanip>
#include <cmath>
#include <algorithm>
#include <numeric>
#include <vector>
#include <string>
#include <cstdio>
#include <cstring>
using namespace std;
double a, b, c, d;

int main() {
	cin >> a;
	b = pow(5.0, 0.5);
	c = pow((1.0 + b) / 2, a);
	d = pow((1.0 - b) / 2, a);
	printf("%.2f", (c - d ) / b);
}