// github.com/Johniel/contests // yukicoder/2070/main.cpp #include #define each(i, c) for (auto& i : c) #define unless(cond) if (!(cond)) // #define endl "\n" using namespace std; template ostream& operator << (ostream& os, pair p) { os << "(" << p.first << "," << p.second << ")"; return os; } template istream& operator >> (istream& is, pair& p) { is >> p.first >> p.second; return is; } template ostream& operator << (ostream& os, vector v) { os << "("; for (auto& i: v) os << i << ","; os << ")"; return os; } template istream& operator >> (istream& is, vector& v) { for (auto& i: v) is >> i; return is; } template ostream& operator << (ostream& os, set s) { os << "#{"; for (auto& i: s) os << i << ","; os << "}"; return os; } template ostream& operator << (ostream& os, map m) { os << "{"; for (auto& i: m) os << i << ","; os << "}"; return os; } template istream& operator >> (istream& is, array& a) { for (auto& i: a) is >> i; return is; } template ostream& operator << (ostream& os, array& a) { os << "[]{"; for (auto& i: a) os << i << ","; os << "}"; return os; } template inline T setmax(T& a, T b) { return a = std::max(a, b); } template inline T setmin(T& a, T b) { return a = std::min(a, b); } using lli = long long int; using ull = unsigned long long; using str = string; template using vec = vector; constexpr array di({0, 1, -1, 0, 1, -1, 1, -1}); constexpr array dj({1, 0, 0, -1, 1, -1, -1, 1}); constexpr lli mod = 1e9 + 7; // constexpr lli mod = 998244353; int main(int argc, char *argv[]) { ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.setf(ios_base::fixed); cout.precision(15); double a; while (cin >> a) { cout << (15 + 5 * sqrt(5)) / 12.0 * a * a * a << endl; } return 0; }