#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

 }