#include "bits/stdc++.h"
#pragma GCC optimize("Ofast")

// Begin Header {{{
#pragma region
using namespace std;

#ifndef DEBUG
#define dump(...)
#endif

#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define rep(i, b, e) for (intmax_t i = (b), i##_limit = (e); i < i##_limit; ++i)
#define repc(i, b, e) for (intmax_t i = (b), i##_limit = (e); i <= i##_limit; ++i)
#define repr(i, b, e) for (intmax_t i = (b), i##_limit = (e); i >= i##_limit; --i)
#define var(Type, ...) \
    Type __VA_ARGS__;  \
    input(__VA_ARGS__)
#define let const auto

constexpr size_t operator""_zu(unsigned long long value) {
    return value;
};
constexpr intmax_t operator""_jd(unsigned long long value) {
    return value;
};
constexpr uintmax_t operator""_ju(unsigned long long value) {
    return value;
};

constexpr int INF = 0x3f3f3f3f;
constexpr intmax_t LINF = 0x3f3f3f3f3f3f3f3f_jd;

using usize = size_t;
using imax = intmax_t;
using uimax = uintmax_t;
using ld = long double;

template <class T, class Compare = less<>>
using MaxHeap = priority_queue<T, vector<T>, Compare>;
template <class T, class Compare = greater<>>
using MinHeap = priority_queue<T, vector<T>, Compare>;

inline void input() {}
template <class Head, class... Tail>
inline void input(Head&& head, Tail&&... tail) {
    cin >> head;
    input(forward<Tail>(tail)...);
}

template <class Container, class Value = typename Container::value_type,
          enable_if_t<!is_same<Container, string>::value, nullptr_t> = nullptr>
inline istream& operator>>(istream& is, Container& vs) {
    for (auto& v: vs) is >> v;
    return is;
}

template <class T, class U>
inline istream& operator>>(istream& is, pair<T, U>& p) {
    is >> p.first >> p.second;
    return is;
}

inline void output() {
    cout << "\n";
}
template <class Head, class... Tail>
inline void output(Head&& head, Tail&&... tail) {
    cout << head;
    if (sizeof...(tail)) cout << " ";
    output(forward<Tail>(tail)...);
}

template <class Container, class Value = typename Container::value_type,
          enable_if_t<!is_same<Container, string>::value, nullptr_t> = nullptr>
inline ostream& operator<<(ostream& os, const Container& vs) {
    static constexpr const char* delim[] = {" ", ""};
    for (auto it = begin(vs); it != end(vs); ++it) {
        os << delim[it == begin(vs)] << *it;
    }
    return os;
}

template <class Iterator>
inline void join(const Iterator& Begin, const Iterator& End, const string& delim = "\n",
                 const string& last = "\n") {
    for (auto it = Begin; it != End; ++it) {
        cout << ((it == Begin) ? "" : delim) << *it;
    }
    cout << last;
}

template <class T>
inline vector<T> makeVector(const T& init_value, size_t sz) {
    return vector<T>(sz, init_value);
}

template <class T, class... Args>
inline auto makeVector(const T& init_value, size_t sz, Args... args) {
    return vector<decltype(makeVector<T>(init_value, args...))>(
        sz, makeVector<T>(init_value, args...));
}

template <class Func>
class FixPoint : Func {
public:
    explicit constexpr FixPoint(Func&& f) noexcept : Func(forward<Func>(f)) {}

    template <class... Args>
    constexpr decltype(auto) operator()(Args&&... args) const {
        return Func::operator()(*this, std::forward<Args>(args)...);
    }
};

template <class Func>
static inline constexpr decltype(auto) makeFixPoint(Func&& f) noexcept {
    return FixPoint<Func> {forward<Func>(f)};
}

template <class Container>
struct reverse_t {
    Container& c;
    reverse_t(Container& c) : c(c) {}
    auto begin() {
        return c.rbegin();
    }
    auto end() {
        return c.rend();
    }
};

template <class Container>
auto reversed(Container& c) {
    return reverse_t<Container>(c);
}

template <class T>
inline bool chmax(T& a, const T& b) noexcept {
    return b > a && (a = b, true);
}

template <class T>
inline bool chmin(T& a, const T& b) noexcept {
    return b < a && (a = b, true);
}

template <class T>
inline T diff(const T& a, const T& b) noexcept {
    return a < b ? b - a : a - b;
}

template <class T>
inline T sigma(const T& l, const T& r) noexcept {
    return (l + r) * (r - l + 1) / 2;
}

template <class T>
inline T ceildiv(const T& n, const T& d) noexcept {
    return (n + d - 1) / d;
}

void operator|=(vector<bool>::reference lhs, const bool rhs) {
    lhs = lhs | rhs;
}

void operator&=(vector<bool>::reference lhs, const bool rhs) {
    lhs = lhs & rhs;
}

void operator^=(vector<bool>::reference lhs, const bool rhs) {
    lhs = lhs ^ rhs;
}

void ioinit() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(10);
    cerr << fixed << setprecision(10);
    clog << fixed << setprecision(10);
}
#pragma endregion
// }}} End Header

int main() {
    ioinit();

    var(ld, N);

    output((15 + 5 * sqrtl(5)) / ld(12) * N * N * N);
    return 0;
}