import java.util.Scanner;

public class Main {
    public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
    	double c = sc.nextDouble();
    	double ri = sc.nextDouble();
    	double ro = sc.nextDouble();
    	double v = Math.pow(Math.PI, 2) * (ri + ro) * Math.pow(ro - ri,2) / 4;
    	System.out.println(v * c);
    }
}