import java.util.Arrays;
import java.util.LinkedList;
import java.util.Scanner;

public class Main {
	
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		final int C = sc.nextInt();
		final double R_in = sc.nextInt();
		final double R_out = sc.nextInt();
		
		final double r = (R_in + R_out) / 2;
		
		System.out.printf("%.8f\n", 2 * Math.PI  * r * (r - R_in) * (r - R_in) * Math.PI * C);
		
	}
	
}