import java.util.*;
import java.util.stream.Stream;
import java.time.*;
import java.time.format.*;

public class No89 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int c=sc.nextInt();
		double in=sc.nextDouble();
		double out=sc.nextDouble();
		System.out.println(c*Math.PI*Math.PI/4*(in+out)*(in-out)*(in-out));
        
	}
}