#include <algorithm> #include <array> #include <bitset> #include <cassert> #include <cctype> #include <chrono> #include <cmath> #include <complex> #include <cstdint> #include <cstdlib> #include <deque> #include <functional> #include <iomanip> #include <iostream> #include <limits> #include <list> #include <map> #include <memory> #include <numeric> #include <queue> #include <random> #include <set> #include <stack> #include <string> #include <type_traits> #include <unordered_map> #include <utility> #include <vector> /* template start */ using i64 = std::int_fast64_t; using u64 = std::uint_fast64_t; #define rep(i, a, b) for (i64 i = (a); (i) < (b); (i)++) #define all(i) i.begin(), i.end() #ifdef LOCAL #define debug(...) \ std::cerr << "LINE: " << __LINE__ << " [" << #__VA_ARGS__ << "]:", \ debug_out(__VA_ARGS__) #else #define debug(...) #endif void debug_out() { std::cerr << std::endl; } template <typename Head, typename... Tail> void debug_out(Head h, Tail... t) { std::cerr << " " << h; if (sizeof...(t) > 0) std::cout << " :"; debug_out(t...); } template <typename T1, typename T2> std::ostream& operator<<(std::ostream& os, std::pair<T1, T2> pa) { return os << pa.first << " " << pa.second; } template <typename T> std::ostream& operator<<(std::ostream& os, std::vector<T> vec) { for (std::size_t i = 0; i < vec.size(); i++) os << vec[i] << (i + 1 == vec.size() ? "" : " "); return os; } template <typename T1, typename T2> inline bool chmax(T1& a, T2 b) { return a < b && (a = b, true); } template <typename T1, typename T2> inline bool chmin(T1& a, T2 b) { return a > b && (a = b, true); } template <typename Num> constexpr Num mypow(Num a, u64 b, Num id = 1) { if (b == 0) return id; Num x = id; while (b > 0) { if (b & 1) x *= a; a *= a; b >>= 1; } return x; } template <typename T> std::vector<std::pair<std::size_t, T>> enumerate(const std::vector<T>& data) { std::vector<std::pair<std::size_t, T>> ret; for (std::size_t index = 0; index < data.size(); index++) ret.emplace_back(index, data[index]); return ret; } /* template end */ int main(){ std::cin.tie(nullptr); std::ios::sync_with_stdio(false); i64 k; std::cin>>k; if(k==0){ constexpr long double PI = 3.14159265l; std::cout<<std::setprecision(10)<<PI*PI/6<<"\n"; return 0; } long double ans=0; rep(i,1,k+1)ans+=1.0l/i; ans/=(long double)k; std::cout<<std::setprecision(10)<<ans<<"\n"; return 0; }