Problem: One day, as Sherlock Holmes was tracking down one very important criminal, he found a wonderful painting on the wall. This wall could be represented as a plane. The painting had several concentric circles that divided the wall into several parts. Some parts were painted red and all the other were painted blue. Besides, any two neighboring parts were painted different colors, that is, the red and the blue color were alternating, i. e. followed one after the other. The outer area of the wall (the area that lied outside all circles) was painted blue. Help Sherlock Holmes determine the total area of red parts of the wall.

Let us remind you that two circles are called concentric if their centers coincide. Several circles are called concentric if any two of them are concentric.

Input

The first line contains the single integer n (1 ≤ n ≤ 100). The second line contains n space-separated integers ri (1 ≤ ri ≤ 1000) — the circles' radii. It is guaranteed that all circles are different.

Output

Print the single real number — total area of the part of the wall that is painted red. The answer is accepted if absolute or relative error doesn't exceed 10 - 4.

Examples

Input

1
1


Output

3.1415926536


Input

3
1 4 2


Output

40.8407044967

Note

In the first sample the picture is just one circle of radius 1. Inner part of the circle is painted red. The area of the red part equals π × 12 = π.

In the second sample there are three circles of radii 1, 4 and 2. Outside part of the second circle is painted blue. Part between the second and the third circles is painted red. Part between the first and the third is painted blue. And, finally, the inner part of the first circle is painted red. Overall there are two red parts: the ring between the second and the third circles and the inner part of the first circle. Total area of the red parts is equal (π × 42 - π × 22) + π × 12 = π × 12 + π = 13π

Solution (in JAVA):

Solution:
import java.util.*;
import java.io.*;
public class Trace
{

	/************************ SOLUTION STARTS HERE ************************/

	//DONT FORGET TO COMMIT AND PUSH TO GITHUB

	private static void solve(FastScanner s1, FastWriter out){

		int len = s1.nextInt();
		int radius[] = new int[len+1];
		for(int i=1;i<=len;i++)
			radius[i] = s1.nextInt();
		
		double totalArea = 0.0;
		Arrays.parallelSort(radius);
		for(int i = len;i>0;i-=2)
		{
			double currArea = Math.PI * ((double) ((radius[i] * radius[i] ) - (radius[i-1] * radius[i-1])));
			totalArea += currArea;
		}
		out.print(totalArea);
	}

	/************************ SOLUTION ENDS HERE ************************/



	/************************ TEMPLATE STARTS HERE ************************/

	public static void main(String []args) throws IOException {
		FastScanner in  = new FastScanner(System.in);
		FastWriter  out = new FastWriter(System.out);
		solve(in, out);
		in.close();
		out.close();
	}    

	static class FastScanner{
		public BufferedReader reader;
		public StringTokenizer st;
		public FastScanner(InputStream stream){
			reader = new BufferedReader(new InputStreamReader(stream));
			st = null;
		}
		public String next(){
			while(st == null || !st.hasMoreTokens()){
				try{
					String line = reader.readLine();
					if(line == null) return null;
					st = new StringTokenizer(line);
				}catch (Exception e){
					throw (new RuntimeException());
				}
			}
			return st.nextToken();
		}
		public String nextLine(){
			String str = null;
			try {
				str = reader.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}
		public int nextInt(){
			return Integer.parseInt(next());
		}
		public long nextLong(){
			return Long.parseLong(next());
		}
		public double nextDouble(){
			return Double.parseDouble(next());
		}
		int[] nextIntArray(int n) {
			int[] arr = new int[n];
			for (int i = 0; i < n; i++) {
				arr[i] = nextInt();
			}
			return arr;
		}

		long[] nextLongArray(int n) {
			long[] arr = new long[n];
			for (int i = 0; i < n; i++) {
				arr[i] = nextLong();
			}
			return arr;
		}
		public void close(){	
			try{ reader.close(); } catch(IOException e){e.printStackTrace();}
		}
	}
	static class FastWriter{
		BufferedWriter writer;
		public FastWriter(OutputStream stream){
			writer = new BufferedWriter(new OutputStreamWriter(stream));
		}
		public void print(int i) {
			print(Integer.toString(i));
		}
		public void println(int i) {
			print(Integer.toString(i));
			print('\n');
		}
		public void print(long i) {
			print(Long.toString(i));
		}
		public void println(long i) {
			print(Long.toString(i));
			print('\n');
		}
		public void print(double i) {
			print(Double.toString(i));
		}
		public void print(boolean i) {
			print(Boolean.toString(i));
		}
		public void print(char i) {
			try{writer.write(i);} catch(IOException e){e.printStackTrace();}
		}
		public void print(String s){
			try{writer.write(s);} catch(IOException e){e.printStackTrace();}
		}
		public void println(String s){
			try{writer.write(s);writer.write('\n');} catch(IOException e){e.printStackTrace();}
		}
		public void println(){
			try{writer.write('\n');} catch(IOException e){e.printStackTrace();}
		}
		public void print(int arr[])
		{
			for (int i = 0; i < arr.length; i++) {
				print(arr[i]);
				print(' ');
			}
		}
		public void close(){
			try{writer.close();} catch(IOException e){e.printStackTrace();}
		}
	}

	/************************ TEMPLATE ENDS HERE ************************/
}