#pragma GCC optimize("O3")
#include <algorithm>

#include <bits/stdc++.h>
#define ll long long
#define rep(i,n) for(ll i=0;i<(n);i++)
#define pll pair<ll,ll>
#define pii pair<int,int>
#define pq priority_queue
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define endl '\n'
#define ios ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
#define lb(c,x) distance(c.begin(),lower_bound(all(c),x))
#define ub(c,x) distance(c.begin(),upper_bound(all(c),x))

using namespace std;



template<class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}

const int INF=1e9;

const double pi=acos(-1);

int main(){
    int k;
    cin >> k;
    if(k==0){
        cout << setprecision(30) << fixed;
        double ans=pi*pi/6.0;
        cout << ans << endl;
        return 0;
    }
    double ans=0.0;
    for(int i=1;i<=k;i++){
        double c=i;
        ans+=1.0/c;
    }
    double p=k;
    ans/=p;
    cout << setprecision(30) << fixed;
    cout << ans << endl;
    return 0;
}