#include<bits/stdc++.h> using namespace std; int main(){ int n,fz=2,fm=1,t; double sum=0; cin>>n; for(int i=1;i<=n;i++){ sum += fz*1.0/fm; t = fm; fm = fz; fz = fz+t; } printf("%.4lf",sum); return 0; }