#include<iostream>
#include<cstdio>
using namespace std;
double fei(double m)
{
	if(m==1||m==2)
	return 1;
	else
	return fei(m-1)+fei(m-2);
}
int main()
{
double sum=0,n;
int i;
cin>>n;
for(i=1;i<=n;i++)
{
sum+=(double)(fei(i+2)/fei(i+1));	
}
printf("%.4lf",sum);
}