#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)

const double PI = acos(-1);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  double a, b, c;
  cin >> c >> a >> b;

  double r = (b - a) / 2;
  double l = (b + a) / 2;
  cout << fixed << setprecision(10) << c * (PI * r * r) * 2 * PI * l << endl;
  
  return 0;
}