import java.util.*;

public class Yukicoder_89{
	public static void main(String[] args){
		Scanner stdIn = new Scanner(System.in);
		int C = stdIn.nextInt();
		int R_in = stdIn.nextInt();
		int R_out = stdIn.nextInt();
		double vol = Math.pow((R_out-R_in)/2.0,2)*Math.PI*((R_out-R_in)/2.0+R_in)*2.0*Math.PI;
		System.out.println(vol*C);
	}
}