#include <bits/stdc++.h>
#define rep(i, ss, ee) for (int i = ss; i < ee; ++i)
using namespace std;
const double PI = 3.14159265358979323846;

void solve() {
  int c, a, b;
  cin >> c >> a >> b;
  double ans = c / 4.0 * PI * PI * (a + b) * (b - a) * (b - a);
  cout << ans << endl;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(12);
  solve();
  getchar();
}