#include <iostream>
#include <list>
#include <vector>
#include <string>
#include <stdio.h>
#include <stdint.h>
#include <iomanip>
using namespace std;

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

#define CIN( LL , A ) LL A; cin >> A 
#define GETSEGMENT( A , SEPARATOR ) string A; getline( cin , A , SEPARATOR ) 
#define GETLINE( A ) string A; getline( cin , A ) 
#define FOR_LL( 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 RETURN( LL , ANSWER ) const LL answer_for_contest = ( ANSWER ); cout << answer_for_contest << endl; return 0 
#define DOUBLE( DIGITS , ANSWER ) const double answer_for_contest = ( ANSWER ); cout << fixed << setprecision( DIGITS ) << answer_for_contest << endl; return 0 

template <typename T> inline T Distance( const T& a , const ll& b ){ return a < b ? b - a : a - b; }

int main()
{

  CIN( ll , C );
  CIN( ll , Rin );
  CIN( ll , Rout );

  // integral( real r , w , theta ; ( r - ( Rin + Rout ) / 2 ) ^ 2 + w ^ 2 <= ( ( Rout - Rin ) / 2 ) ^ 2  && 0 <= theta && theta < 2 * pi ; r++ , w++ , theta++ ) r dr dw dtheta
  // = 2 * pi * integral( real r ; Rin <= r && r <= Rout ; r++ ) 2 * r * sqrt( ( ( Rout - Rin ) / 2 ) ^ 2 - ( r - ( Rin + Rout ) / 2 ) ^ 2 ) dr
  // = 2 * pi *
  //    (
  //      difference( - ( 2 / 3 ) * ( ( ( Rout - Rin ) / 2 ) ^ 2 - ( X - ( Rin + Rout ) / 2 ) ^ 2 ) ^ ( 3 / 2 ) , Rin , Rout ]
  //      - integral( real r ; Rin <= r && r <= Rout ; r++ ) - ( Rin + Rout ) * sqrt( ( ( Rout - Rin ) / 2 ) ^ 2 - ( r - ( Rin + Rout ) / 2 ) ^ 2 ) dr
  //    )
  // = 2 * pi * ( 0 + ( Rin + Rout ) * pi * ( ( Rout - Rin ) / 2 ) ^ 2 / 2 )
  // = ( Rin + Rout ) * ( Rout - Rin ) ^ 2 * pi ^ 2 / 4
  DOUBLE( 6 , ( C * ( Rin + Rout ) * ( Rout - Rin ) * ( Rout - Rin ) ) * ( 3.1415926535898 * 3.1415926535898 ) / 4.0 );

}