#include <iostream>
#include <queue>
#include <stack>
#include <cstdio>
#include <vector>
#include <map>
#include <set>
#include <bitset>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <cstdlib>
#include <string>
#include <sstream>
#include <time.h>
#define x first
#define y second
#define pb push_back
#define mp make_pair
#define lson l,m,rt*2
#define rson m+1,r,rt*2+1
#define mt(A,B) memset(A,B,sizeof(A))
#define mod 1000000007
using namespace std;
typedef long long LL;
const double PI = acos(-);
const int N=2e5+;
const int inf = 0x3f3f3f3f;
const LL INF=0x3f3f3f3f3f3f3f3fLL;
//已知圆锥的表面积S求最大的体积：V=S*sqrt(S/(72*PI))
int main()
{
#ifdef Local
freopen("data.txt","r",stdin);
#endif
double n;
cin>>n;
printf("%lf\n",n*sqrt(n/(*PI)));
#ifdef Local
cerr << "time: " << (LL) clock() * / CLOCKS_PER_SEC << " ms" << endl;
#endif
}