#include<iostream>
#include<map>
#include<vector>
#include <algorithm>
#include<math.h>
#include <iomanip>
#include<set>
#include <numeric>
#include<string>
using namespace std;

int main()
{
    int k;
    cin >> k;
    double sum1 = 0;
    for (int i = 1; i <= k; i++){
        sum1 += 1./i;
    }
    cout << fixed << setprecision(8);
    if (k == 0) cout << M_PI*M_PI/6 << endl;
    else cout << sum1/k << endl;
}