#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,p=1,q=2,temp=0;
    cin>>n;
    double a[n],sum=0.0;
    for(int i=0;i<n;i++){
        a[i]=q/p*1.0;
        sum+=a[i];
        temp = q;
        q = p+q;
        p = temp;
    }
    printf("%.4lf",sum);
    return 0;
}