#include<iostream> using namespace std; double fz1=2,fm1=1; double fz2=3,fm2=2; int n; int main () { 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; }