import java.util.*;
import static java.lang.System.*;

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