import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    double c = sc.nextDouble();
    double rin = sc.nextDouble();
    double rout = sc.nextDouble();
    double r = (rout - rin) / (double)2;
    double ans = Math.PI * r * r * 2 * Math.PI * (r + rin) * c;
    System.out.println(ans);
  }
}