import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner koko = new Scanner(System.in);
        double cal = koko.nextDouble();
        double in = koko.nextDouble();
        double out = koko.nextDouble();
        double r = (out-in)/2;
        double cen = in+r;
        double vol = r*r*Math.PI*2*cen*Math.PI;
        double ans = vol*cal;
        System.out.println(ans);
    }
}