#include<iostream>
#include<cmath>
#include<iomanip>
#define REP(i,a,b) for(int i=(int)(a);i<(int)(b);++i)

using namespace std;

int main(){
  int C, Rin, Rout;
  const double Pi = acos(-1);
  cin >> C >> Rin >> Rout;
  double r = (Rout - Rin) / 2.0;
  cout << fixed << setprecision(10) << 2 * (Rin + r) * Pi * r * r * Pi * C << endl;
  return 0;
}