#include<bits/stdc++.h>
using namespace std;
#define int long long
#define ii pair <int, int>
#define app push_back
#define all(a) a.begin(), a.end()
#define bp __builtin_popcountll
#define ll long long
#define mp make_pair
#define f first
#define s second
#define Time (double)clock()/CLOCKS_PER_SEC
#define debug(x) std::cout << #x << ": " << x << '\n';
signed main() {
    #ifdef HOME
    freopen("input.txt", "r", stdin);
    #else
    #define endl '\n'
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    cout.setf(ios::fixed); cout.precision(20); 
    #endif
    #define double long double
    
    int k;
    cin >> k;

    if (k == 0) {
        const double PI = acos(-1);
        cout << PI * PI / 6 << endl;
        exit(0);
    }   

    double ans = 0;
    for (int i = 1; i <= k; ++i)
        ans += 1.0/i;
    cout << ans/k << endl;

}