package 練習;
import java.util.Date;
import java.util.Scanner;

public class main{
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);
		long exec_time=new Date().getTime();
		double c=sc.nextDouble();
		double r_in=sc.nextDouble();
		double r_out=sc.nextDouble();
		
		double V;
		V=Math.PI*2*((r_out+r_in)/2)*Math.pow((r_out-r_in)/2,2)*Math.PI;
		System.out.println(V*c);
		System.err.println(new Date().getTime()-exec_time+"ms");
	}
}