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.io.BufferedReader;
import java.text.DecimalFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;
import java.io.*;

public class abc {
	static PrintWriter pw;

	static class FastReader {
		BufferedReader br;
		StringTokenizer st;

		public FastReader() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	}

	public static long gcd(long a, long b) {
		return b == 0 ? a : gcd(b, a % b);
	}

	public static boolean isPrime(long n) {
		if (n == 2)
			return true;
		long i = 2;
		while (i * i <= n) {
			if (n % i == 0)
				return false;
			i++;
		}
		return true;
	}

	public static long[] remove(long n) {
		long res[] = new long[1000000000];
		long rese = 0;
		int i = 0;
		while (n > 0) {
			long dig = n % 10;
			n = n / 10;
			if (dig > 0) {
				rese = dig;
				res[i++] = rese;
			}
		}
		return res;
	}

	static int ceil(int x, int y) {
		return (x % y == 0 ? x / y : (x / y + 1));
	}

	static long ceil(long x, long y) {
		return (x % y == 0 ? x / y : (x / y + 1));
	}

	static int max(int x, int y) {
		return Math.max(x, y);
	}

	static int min(int x, int y) {
		return Math.min(x, y);
	}

	static int abs(int x) {
		return Math.abs(x);
	}

	static long abs(long x) {
		return Math.abs(x);
	}

	static int log2(int N) {
		int result = (int) (Math.log(N) / Math.log(2));
		return result;
	}

	static long max(long x, long y) {
		return Math.max(x, y);
	}

	static long min(long x, long y) {
		return Math.min(x, y);
	}

	public static class pair {
		int x;
		int y;

		public pair(int a, int b) {
			x = a;
			y = b;
		}
	}

	public static class Comp implements Comparator<pair> {
		public int compare(pair a, pair b) {
			if (a.x != b.x) {
				return a.x - b.x;
			} else {
				return a.y - b.y;
			}
		}
	}

	public static void extract(ArrayList<Integer> ar, int k, int d) {
		int c = 0;
		for (int i = 1; i < k; i++) {
			int x = 0;
			boolean dm = false;
			while (x > 0) {
				long dig = x % 10;
				x = x / 10;
				if (dig == d) {
					dm = true;
					break;
				}
			}
			if (dm)
				ar.add(i);
		}
	}

	public static void dfs(int index, boolean vis[], int a[], int b[], int n) {
		vis[index] = true;
		for (int i = 0; i < n; i++) {
			if (!vis[i] && (a[i] == a[index] || b[i] == b[index]))
				dfs(i, vis, a, b, n);
		}
	}
// counts the set(1) bit of a number
	public static long countSetBitsUtil(long x) {
		if (x <= 0)
			return 0;
		return (x % 2 == 0 ? 0 : 1) + countSetBitsUtil(x / 2);
	}
	
//tells whether a particular index has which bit of a number	
	public static int getIthBitsUtil(int x , int y)
	{
		return (x&(1<<y))!=0 ? 1 : 0;
	}
	
	public static void swap(long x,long y) {
		x=x^y;
		y=y^x;
		x=x^y;
	}
	
	public static double decimalPlaces(double sum) {
		DecimalFormat df = new DecimalFormat("#.00");
		String angleFormated = df.format(sum);
		double fin = Double.parseDouble(angleFormated);
		return fin;
	}

//use collections.swap for swapping 
	static boolean isSubSequence(String str1, String str2, int m, int n) {
		int j = 0;

		for (int i = 0; i < n && j < m; i++)
			if (str1.charAt(j) == str2.charAt(i))
				j++;

		return (j == m);
	}

	static long[] sum(int k, long n) {
		long a[] = new long[k];
		int c = 0;
		while (n > 0) {
			a[c++] = n % 10;
			n = n / 10;
		}
		return a;
	}

	static long pow(long base, long power) {
		if (power == 0) {
			return 1;
		}
		long result = pow(base, power / 2);
		if (power % 2 == 1) {
			return result * result * base;
		}
		return result * result;
	}

	public static void main(String[] args) throws Exception {

		FastReader sc = new FastReader();
		pw = new PrintWriter(System.out);

		// use arraylist as it use the concept of dynamic table(amortized analysis)
		// Arrays.stream(array).forEach(a -> Arrays.fill(a, 0));
		int t=1;
        while(t-->0)
        {
        	int n=sc.nextInt();
        	int a[]=new int[n];
        	for(int i=0;i<n;i++)
        		a[i]=sc.nextInt();
        	double pi=3.1415926536;
        	double sum=0;
        	Arrays.sort(a);
        	int c=0;
        	if(n%2!=0)
        		{
        			c=1;
        			sum=Math.pow(a[0], 2);
        		}
        	for(int i=1;i<n;i++)
        	{
        		if(c%2==0)
        			{
        				
        				sum+=(a[i]*a[i]-a[i-1]*a[i-1]);
        			}
        		c++;
        	}
        	pw.println(pi*sum);
        }
		pw.flush();
	}
}