#include <bits/stdc++.h>
//---------------------------
using namespace std;
//---------------------------
#define REP(i,n) for(int i = 0; i < (n); i++)
#define P(x) cout << (x) << "\n"
//---------------------------

double torus(int r1,int r2){
  double p = 3.14159265358979323846;
  int r = r2 - r1;
  int rr = r2 + r1;
  double a = (p * p * rr * r * r )/ 4.0;
  return a;
}

int main(){
  std::ios::sync_with_stdio(false);
  std::cin.tie(0);



  int c,x,y;cin >> c >> x >> y;
  double a = c * torus(x,y);
  printf("%.5f\n", a);

  return 0;
}