# include<iostream> # include<cstdio> # include<iomanip> # include<cmath> using namespace std; int main(){ double fz=2,fm=1,s=fz/fm,t; int n; cin>>n; for(int i=2;i<=n;i++){ t=fz; fz=fz+fm; fm=t; s+=fz/fm; } printf("%.4lf",s); return 0; }