#include<iostream>
#include<vector>
#include<cmath>
#include<iomanip>
#define ll long long

const long double PI = acosl(-1.0);

using namespace std;

int main(){
    cout << fixed << setprecision(15);
    int n;
    cin >> n;
    if(n == 0){
        cout << PI*PI/6 << endl;
        return 0;
    }
    long double sum = 0;
    for(int i = 1;i <= n;i++){
        long double x = 1/(long double)i;
        sum += x;
    }
    sum /= (long double)n;
    cout << sum << endl;
    return 0;
}