#include <bits/stdc++.h>
using namespace std;
const double PI = acos(-1);
int main(){
  cout << fixed << setprecision(10);
  int C, R1, R2;
  cin >> C >> R1 >> R2;
  double r = (R2 - R1) / 2;
  cout << 2 * PI * (R1 + r) * (PI * r * r) * C << endl;
}