#include <iostream> // #include <bits/stdc++.h> using namespace std; int main() { double fz1 = 2,fm1 = 1; double fz2 = 3,fm2 = 2; int n; cin>>n; if (n == 1) { printf("%.4lf",2.0000); }else if (n == 2) { printf("%.4lf",fz1/fm1 + fz2/fm2); }else { double sum = fz1/fm1 + fz2/fm2; for (int i = 3; i <= n;i++) { double fzi = fz1+fz2; double fmi = fm1+fm2; sum += fzi/fmi; fz1 = fz2; fz2 = fzi; fm1 = fm2; fm2 = fmi; } printf("%.4lf",sum); } return 0; } // // 2 3 5 8 13 // fz1 fz2 fzi // fz1 fz2 fzi // fz1 fz2 fzi