#include <bits/stdc++.h>
#define fastIO (cin.tie(0), cout.tie(0), ios::sync_with_stdio(false))
#define precise(i) fixed << setprecision(i)
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
using namespace std;

int main() {
  fastIO;
  double c, l, r;
  cin >> c >> l >> r;
  double v = M_PI * M_PI * (l + r) * (l - r) * (l - r) / 4.0;

  cout << precise(8) << v * c << endl;

  return 0;
}