#include<bits/stdc++.h> using namespace std;

int main(){ int m,n,i; double sum=0; cin>>n; int p=1,q=2; int pr=1,qr=2; i=2; sum=2; while(i<=n){ p=qr; q=pr+qr; pr=p; qr=q; sum=sum+1.0*q/p; i=i+1; } cout<<fixed<<setprecision(4)<<sum; return 0; }