import java.math.*;
import java.util.*;


public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int c=sc.nextInt();
		int rin = sc.nextInt();
		int rout=sc.nextInt();
		double men = (rout*1.0-rin)/2*(rout*1.0-rin)/2*Math.PI;
		double kyori = (rout*1.0+rin)/2*2*Math.PI;
		System.out.println(men*kyori*c);
	}
}