import java.util.*;

public class Exercise135{
  public static void main (String[] args){

    Scanner sc = new Scanner(System.in);

    double c = sc.nextDouble();
    double rIn = sc.nextDouble();
    double rOut = sc.nextDouble();

    System.out.println(c * ((rOut - rIn) * (rOut - rIn) * Math.PI * (rOut + rIn) / 4 * Math.PI));
  }
}