#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin >> n;
	double a[n];
	a[0] = 1;
	a[1] = 2;
	for(int i=2;i<=n;i++)
		a[i] = a[i-2]+a[i-1];
	double sum = 0;
	for(int i=0;i<n;i++)
		sum += a[i+1]/a[i];
	cout << fixed << setprecision(2) << sum ;	
    return 0;
}