#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int n, r1, r2;
  cin >> n >> r1 >> r2;
  double r = (r2 - r1) / 2.0;
  double R = (r1 + r2) / 2.0;
  const double Pi = acos(-1);
  double ans = (r * r * Pi) * (2 * Pi * R) * n;
  cout << fixed << setprecision(15) << ans << endl;
  return 0;
}