// #define _GLIBCXX_DEBUG 
#include<bits/stdc++.h>
using namespace std;

using uint = unsigned int;
using ll = long long;

#define CIN( LL , A ) LL A; cin >> A 
#define GETLINE( A ) string A; getline( cin , A ) 
#define GETLINE_SEPARATE( A , SEPARATOR ) string A; getline( cin , A , SEPARATOR ) 
#define UNTIE ios_base::sync_with_stdio( false ); cin.tie( nullptr ) 
#define FOR( VAR , INITIAL , FINAL_PLUS_ONE ) for( ll VAR = INITIAL ; VAR < FINAL_PLUS_ONE ; VAR ++ ) 
#define FOR_ITR( ARRAY , ITR , END ) for( auto ITR = ARRAY .begin() , END = ARRAY .end() ; ITR != END ; ITR ++ ) 
#define REPEAT( HOW_MANY_TIMES ) FOR_LL( VARIABLE_FOR_REPEAT , 0 , HOW_MANY_TIMES ) 
#define RETURN( ANSWER ) cout << ( ANSWER ) << endl; return 0 
#define DOUBLE( PRECISION , ANSWER ) cout << fixed << setprecision( PRECISION ) << ( ANSWER ) << endl; return 0 
#define MIN( A , B ) A < B ? A : B;
#define MAX( A , B ) A < B ? B : A;

template <typename T> inline T Absolute( const T& a ){ return a > 0 ? a : - a; }


int main()
{
  CIN( ll , N );
  DOUBLE( 6 , N * N * N * 26.1803399 / 12.0 );

}