#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define rep2(i,m,n) for (int i = (m); i < (n); ++i)
#define rep(i,n) rep2(i,0,n)
#define debug(x) cout << x << endl;
typedef long long int ll;
typedef long double ld;
typedef pair<int, int> P;
template<typename T> struct V : vector<T> { using vector<T>::vector; };
V() -> V<int>;
V(size_t) -> V<int>;
template<typename T> V(size_t, T) -> V<T>;
template<typename T> vector<T> make_vec(size_t n, T a) { return vector<T>(n, a); }
template<typename... Ts> auto make_vec(size_t n, Ts... ts) { return vector<decltype(make_vec(ts...))>(n, make_vec(ts...)); }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &v) { for (auto &e : v) os << e << ' '; return os; }
struct fast_ios { fast_ios(){ cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
template<typename T> inline bool chmin(T &a, T b) { if (a > b) { a = b; return true; } return false; }
template<typename T> inline bool chmax(T &a, T b) { if (a < b) { a = b; return true; } return false; }
const int INF = 1<<30;
const ll LINF = 1LL<<61;
// const ll MOD = 1000000007;
using mint = modint1000000007;
// ld eps = 1e-7;

int main()
{
    ll k;
    cin >> k;
    ld ans = 0;
    ll n = 1;
    while(n * (n + k) < 1e15)
    {
        ans += (ld)(1) / (ld)(n * (n + k));
        n++;
    }
    cout << ans << endl;
    return 0;
}