#include <bits/stdc++.h>

using namespace std;

const double PI = acos(-1);

int main()
{
  int C;
  int Rin, Rout;

  cin >> C;
  cin >> Rin >> Rout;

  double A = (Rout - Rin) / 2.0;
  double B = (Rin + Rout) / 2.0;

  cout << fixed << setprecision(10);
  cout << A * A * PI * 2 * PI * B * C << endl;
}