#include<bits/stdc++.h> using namespace std; double ss(double x){ if(x==1) return 1; if(x==2) return 2; else return ss(x-1)+ss(x-2); } int main(){ double n,s=0; cin>>n; for(double i=1;i<=n;i++){ s+=ss(i+1)/ss(i); } cout<<s; return 0; }