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
import java.util.* ;
import java.math.*;
import java.io.*;


public class javaTemplate {
	
	 public static final int M = 1000000007 ;
	static FastReader sc = new FastReader();
	//	static Scanner sc = new Scanner(System.in) ;
	
	public static void main(String[] args) {
		
		
int n = sc.nextInt() ;
		int arr[] = new int[n] ;
		
		for(int i = 0 ; i< n ; i++) {
			arr[i] = sc.nextInt() ;
		}
		
		Arrays.sort(arr) ;
		
		double ans = 0 ;
		
		if(n%2 == 0) {
			for(int i  = 1 ; i<n ; i+=2) {
				ans += ((arr[i]*arr[i])-(arr[i-1]*arr[i-1])) * Math.PI ;
			}
		} else {
			ans = (arr[0]*arr[0]*Math.PI) ;
			for(int i  = 2 ; i<n ; i+=2) {
				ans += ((arr[i]*arr[i])-(arr[i-1]*arr[i-1])) * Math.PI ;
			}
		}
		

		
		
		System.out.println(ans);
		
		
			
		
		
	}
	

	





			
	
	
	
	 
	
	


	
	
//_________________________//Template//_____________________________________________________________________
	
	
		//		FAST I/O
		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;
	        }
		}
	
	
		
		
//		Check Perfect Squre
		public static boolean checkPerfectSquare(double number) {   
			
			double sqrt=Math.sqrt(number);   
		
			return ((sqrt - Math.floor(sqrt)) == 0);   
		}   
		
		
		
		
		
	static boolean isPrime(int n) {
	        
	        if (n <= 1) return false;
	  
	        for (int i = 2; i < n; i++) {
	            if (n % i == 0) return false;
	        	}
	  
	        return true;
	    }
		
		
		
		
		// Modulo
		static int mod(int a)
		{
		    return (a%M + M) % M;
		}
		
		
		
		
		
			
			
		
		
		
		//		Palindrom or Not
		static boolean isPalindrome(StringBuilder str, int low, int high) {
					
					while (low < high) {
						if (str.charAt(low) != str.charAt(high)) return false;
					 	low++;
					 	high--;
					}
					return true;
				}
	
	
		// Euler Tortient fx
	static int Phi(int n) {
		
		int count = 0 ;
		for(int i = 1 ; i< n ; i++) {
			if(GCD(i,n) == 1) count ++ ;
		}
		return count ;
	}
	
	
	
		// Integer Sort
		static void sort(int[] a) 
		   {
				ArrayList<Integer> l=new ArrayList<>();
				for (int i:a) l.add(i);
				Collections.sort(l);
				for (int i=0; i<a.length; i++) a[i]=l.get(i);
			}
	
		
		
		
		// Long Sort
		static void sort(long[] a) 
		   {
				ArrayList<Long> l=new ArrayList<>();
				for (long i:a) l.add(i);
				Collections.sort(l);
				for (int i=0; i<a.length; i++) a[i]=l.get(i);
			}
	
	
		
		// boolean Value
		static void value(boolean val)
	    {
	       System.out.println(val ? "YES" : "NO");
	       System.out.flush();
	    }
	
	
		
	
		// GCD
		public static int GCD(int a , int b) {
				if(b == 0) return a ;
				
				return GCD(b, a%b) ;
			}
	
		
		
		
		
		
		// sieve
		public static boolean [] sieveofEratosthenes(int n) {
			
			boolean isPrime[] = new boolean[n+1] ;
			Arrays.fill(isPrime, true);
			isPrime[0] = false ;
			isPrime[1] = false ;
			
			for(int i = 2 ; i * i <= n ; i++) {
				
				for(int j = 2 * i ; j<= n ; j+= i) {
					isPrime[j] = false ;
				}
			}
			
			return isPrime ;
		}
		
		
		
		
		// fastPower
		public static long fastPowerModulo(long a, long b, long n) {
			
			long res = 1 ;
			
			while(b > 0) {
			if((b&1) != 0) {
				res = (res * a % n) % n ;
			}
			
			a = (a % n * a % n) % n ;
			b = b >> 1 ;
			}
			
			return res ;
		}
		
		
		
		
		// check if sorted or not	
		public static boolean isSorted(int[] a)
	    {
	        for (int i = 0; i < a.length - 1; i++)
	        {
	            if (a[i] > a[i + 1]) {
	                return false;
	            }
	        }
	 
	        return true;
	    }
	
	
		
		
		
    	static int LCM(int a, int b)
	    {
	        return (a / GCD(a, b)) * b;
	    }
	

}











