import java.util.Scanner;

public class Main1 {
	public static void main(String[] args) {
		Main1 p = new Main1();
	}

	public Main1() {
		Scanner sc = new Scanner(System.in);
		int c=sc.nextInt();
		int a =sc.nextInt();
		int b =sc.nextInt();
		solve(c,a,b);
	}

	public void solve(int c, int a, int b) {
		double res = Math.PI*Math.PI*Math.pow((b-a)/2.0, 2)*2*(a+(b-a)/2.0)*c;
		System.out.println(res);
	}

}