#include <bits/stdc++.h>
#define ll long long
#define pii pair<int,int>
#define pll pair<ll,ll>
#define vi vector<int>
#define vl vector<ll>
#define mp make_pair
#define pb push_back
#define se second
#define fi first
using namespace std;
void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifndef ONLINE_JUDGE
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif
clock_t startTime;
double getCurrentTime() {
	return (double)(clock() - startTime) / CLOCKS_PER_SEC;
}
ll set_on(int n, int k){
	return (n |= 1 << k);
}
ll set_off(int n, int k){
	return (n &= ~(1UL << k));
}
bool check_bit(int n, int k){
	int bit = (n >> k) & 1U;
	if(bit == 1)
		return true;
	return false;
}
void solve(){
	double n;
	cin>>n;
	double volume = 0;
	volume = 5 * (3 + sqrt(5)) / 12;
	volume *= n*n*n;
	cout<<volume<<endl;
}
int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.precision(20);
	cout<<fixed;
	startTime = clock();
	int t=1;
//	cin>>t;
	while(t--)
		solve();

	return 0;
}