import java.util.Scanner;

public class Main{
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);
		while(sc.hasNext()){
			double c=sc.nextDouble();
			double rin=sc.nextDouble();
			double rout=sc.nextDouble();
			System.out.println(c*2*Math.PI*(rout+rin)/2.0*(rout-rin)*(rout-rin)/4*Math.PI);
		}
	}
}