#include<iostream> #include<cstdio> using namespace std; int main() { int n,z=2,m=1,z1,m1; double sum=0; cin>>n; for(int i=0;i<n;i++){ sum+=z/m*1.0; z1=z; m1=m; z=m1+z1; m=z1; } printf("%.4lf",sum); }