import java.util.Scanner;


public class Main_yukicoder89 {

    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 s = Math.PI * (rout - rin) * (rout - rin) / 4;
        
        System.out.printf("%.6f\n", Math.PI * (rout + rin) * s * c);

        sc.close();
    }
}