#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

int C, Rin, Rout;

int main() {
  cin >> C >> Rin >> Rout;
  double r = (Rout - Rin) / 2.0;
  double S = r * r * M_PI;
  double L = (Rout + Rin) / 2.0 * 2 * M_PI;
  double ans = S * L * C;
  cout << fixed << setprecision(15) << ans << endl; 
  return 0;
}