#include<iostream>
#include<iomanip>
using namespace std;
int main()
{
    int n;
    double sequ=2/1.0;
    cin>>n;
    int p[n],q[n];
    p[0]=1;
    q[0]=2;
    for(int i=1;i<n;i++)
    {
        q[i] = p[i-1] + q[i-1];
        p[i] = q[i-i];
        sequ += 1.0*q[i]/p[i];
    }
    cout<<fixed<<setprecision(4)<<sequ<<endl;
    return 0;
}