import java.util.*;

public class Run {
    public static void main (String arg[]) {
        Scanner scan = new Scanner(System.in);
        byte S = scan.nextByte();
        double Rin = scan.nextByte();
        double Rout = scan.nextByte();

        double V;
        V = Math.pow(Math.PI,2) * (Rin + Rout) * Math.pow(Rout-Rin,2) / 4;
        System.out.println(S*V);
    }
}