import java.awt.Point;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
public class Main {
	public static void main(String[] args) throws NumberFormatException, IOException{
		ContestScanner in = new ContestScanner();
		double c = in.nextDouble();
		double rin = in.nextDouble();
		double rout = in.nextDouble();
		double a = (rin+rout)/2;
		double r = (rout-rin)/2;
		System.out.println(2*Math.PI*Math.PI*a*r*r*c);
	}
}

class MyComp implements Comparator<int[]>{
	public int compare(int[] a, int[] b) {
		return a[0] - b[0];
	}
}

class Reverse implements Comparator<Integer>{
	public int compare(Integer arg0, Integer arg1) {
		return arg1 - arg0;
	}
}

class Node{
	int color;
	boolean checked;
	List<Integer> to = new ArrayList<Integer>();
	public Node(){
		checked = false;
	}
}

//class Node{
//	int id;
//	List<Node> edge = new ArrayList<Node>();
//	public Node(int id){
//		this.id = id;
//	}
//	public void createEdge(Node node){
//		edge.add(node);
//	}
//}

class ContestScanner{
	private BufferedReader reader;
	private String[] line;
	private int idx;
	public ContestScanner() throws FileNotFoundException{
		reader = new BufferedReader(new InputStreamReader(System.in));
	}

	public ContestScanner(String filename) throws FileNotFoundException{
		reader = new BufferedReader(new InputStreamReader(new FileInputStream(filename)));
	}
	
	public String nextToken() throws IOException{
		if(line == null || line.length <= idx){
			line = reader.readLine().trim().split(" ");
			idx = 0;
		}
		return line[idx++];
	}
	public long nextLong() throws IOException, NumberFormatException{
		return Long.parseLong(nextToken());
	}
	public int nextInt() throws NumberFormatException, IOException{
		return (int)nextLong();
	}
	public double nextDouble() throws NumberFormatException, IOException{
		return Double.parseDouble(nextToken());
	}
}