#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#define popcount __builtin_popcount
using namespace std;
using ll=long long;
typedef pair<int, int> P;

int main()
{
    int k; cin>>k;
    double ans=0;
    if(k==0){
        double pi=3.14159265358979;
        printf("%.7lf\n", pi*pi/6);
        return 0;
    }
    for(int i=1; i<=k; i++) ans+=1.0/i;
    ans/=k;
    printf("%.7lf\n", ans);
    return 0;
}