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 PYTHON3):

Solution:
'''
def main():
	from sys import stdin,stdout
if __name__=='__main__':
	main()
'''
#Journey to moon
'''
def main():
	from sys import stdin,stdout
	import collections
	N,I =map(int,stdin.readline().split())
	visited=list(0 for x in range(N))
	G=collections.defaultdict(list)
	groups=[0]
	for _ in range(I):
		a,b=map(int,stdin.readline().split())
		G[a].append(b)
		G[b].append(a)
	q=collections.deque()
	flag=0
	for i in range(N):
		if not visited[i]:
			q.append(i)
			visited[i]=flag+1
			groups[flag]+=1
			while len(q):
				top=q.popleft()
				for j in G[top]:
					if visited[j]!=visited[top]:
						visited[j]=flag+1
						groups[flag]+=1
						q.append(j)
			flag+=1
			groups.append(0)
	counter=0
	for i in range(len(groups)-1):
		for j in range(i+1,len(groups)):
			counter+=groups[i]*groups[j]
	stdout.write(str(counter))
if __name__=='__main__':
	main()
'''
#Djikstra's
'''
import collections
class Graph:
	def __init__(self):
		self.nodes=set()
		self.edges=collections.defaultdict(list)
		self.distances = {}

	def add_node(self, value):
		self.nodes.add(value)

	def add_edge(self, from_node, to_node, distance):
		self.edges[from_node].append(to_node)
		self.edges[to_node].append(from_node)
		self.distances[(from_node, to_node)] = distance
		self.distances[(to_node, from_node)] = distance


def dijsktra(graph, initial):
	visited = {initial: 0}
	path = {}

	nodes = set(graph.nodes)

	while nodes:
		min_node = None
		for node in nodes:
			if node in visited:
				if min_node is None:
					min_node = node
				elif visited[node] < visited[min_node]:
					min_node = node

		if min_node is None:
			break

		nodes.remove(min_node)
		current_weight = visited[min_node]

		for edge in graph.edges[min_node]:
			weight = current_weight + graph.distances[(min_node, edge)]
			if edge not in visited or weight < visited[edge]:
				visited[edge] = weight
				path[edge] = min_node

	return visited, path

def main():
	from sys import stdin,stdout
	for _ in range(int(stdin.readline())):
		n,m=map(int,stdin.readline().split())
		G=Graph()
		for i in range(n):
			G.add_node(i+1)
		for i in range(m):
			a,b,c=map(int,stdin.readline().split())
			G.add_edge(a,b,c)
		initial=int(stdin.readline())
		v,p=dijsktra(G, initial)
		#print(v)
		#print(p)
		for i in range(1,n+1):
			if i!=initial:
				k=v.get(i,-1)
				stdout.write(str(k)+' ')
		stdout.write('\n')
if __name__=='__main__':
	main()
'''
#Larget pallindrome in String
'''
def main():
	from sys import stdin,stdout
	string=stdin.readline().strip()
	l=len(string)
	#Triangle logic	
	
	arrlen=(l*(l-1))//2
	arr=list(0 for x in range(arrlen))
	f=0
	c=l-1
	for i in range(l-1):
		for j in range(i+1,l):
			if string[i]==string[j]:
				arr[f+j-i-1]=1
		f+=c
		c-=1
	#print(arr)
	if any(arr):
		
	else:
		if l & 1:
			stdout.write('First')
		else:
			stdout.write('Second')
	#2-d Array Logic
	arr=list(list(0 for i in range(l)) for j in range(l))
	for i in range(l):
		for j in range(l):
			if string[i]==string[j]:
				arr[i][j]=1
	maxim=0
	for i in range(0,l*(l-1)-2,l+1):
		a,b=i+1,i+2
		#print(a,b)
		acount=0
		x=a//5
		y=a%5
		acount=arr[x][y]		
		x-=1
		y-=1
		while x>=0 and y>=0:
			acount+=arr[x][y]
			x-=1
			y-=1
		x=b//5
		y=b%5
		bcount=arr[x][y]		
		x-=1
		y-=1
		while x>=0 and y>=0:
			bcount+=arr[x][y]
			x-=1
			y-=1
		maxim=max((acount,bcount,maxim))
	maxim=max(maxim,arr[l-2][l-1])
	maxim=(maxim<<1)^1
	delta=l-maxim
	if delta & 1:
		stdout.write('Second')
	else:
		stdout.write('First')
if __name__=='__main__':
	main()
'''
#276B
'''
def main():
	from sys import stdin,stdout
	import collections
	s=stdin.readline().strip()
	count=collections.Counter(s)
	l=list(filter(lambda x: count[x] & 1,list(x for x in count)))
	removed=sum(list(count[x] for x in l))-max(list(count[x] for x in l)+[0])
	if removed & 1:
		stdout.write('Second')
	else:
		stdout.write('First')
if __name__=='__main__':
	main()
'''
#362B
'''
def main():
	from sys import stdin,stdout
	n,m=map(int,stdin.readline().split())
	if m:
		dirty=sorted(map(int,stdin.readline().split()))
		if dirty[0]==1 or dirty[-1]==n:
			stdout.write('NO')
		else:
			flag=True
			for i in range(m-2):
				if dirty[i+1]==dirty[i]+1 and dirty[i+2]==dirty[i]+2:
					flag=False
					break
			if flag:
				stdout.write('YES')
			else:
				stdout.write('NO')
	else:
		stdout.write('YES')
if __name__=='__main__':
	main()
'''
#279B SUM OF SUB-ARRAY
'''
def main():
	from sys import stdin,stdout
	n,t=map(int,stdin.readline().split())
	arr=list(map(int,stdin.readline().split()))
	maxim=0
	curr_sum=arr[0]
	i=0
	j=1
	if curr_sum <=t:
		count=1
	else:
		curr_sum=0
		count=0
		i=1
		j=2
	while j<n:
		if curr_sum+arr[j]<=t:
			count+=1
			curr_sum+=arr[j]
			j+=1
		else:
			maxim=max(count,maxim)
			if curr_sum:
				curr_sum-=arr[i]
				count-=1
			else:
				j+=1
			i+=1
	maxim=max(count,maxim)
	stdout.write(str(maxim))
if __name__=='__main__':
	main()
'''
#469B
'''
def main():
	from sys import stdin,stdout
	p,q,l,r=map(int,stdin.readline().split())
	a=[]
	b=[]
	visited=list(0 for x in range(r-l+1))
	#print(visited)	
	for i in range(p):
		x,y=map(int,stdin.readline().split())
		a.append(x)
		b.append(y)
	for i in range(q):
		x,y=map(int,stdin.readline().split())
		x+=l
		y+=l
		for j in range(p):
			#print('x=',x,'y=',y)
			lower=max(0,a[j]-y)
			upper=min(b[j]-x,r)+1
			if upper > lower:
				delta=upper-lower
				#print('upper=',upper,'lower=',lower)
				visited[lower:upper]=list(1 for x in range(delta))
				#print('visited:\n',visited)
	#	print(visited)
	stdout.write(str(visited[:r-l+1].count(1)))
if __name__=='__main__':
	main()
'''
'''
def main():
	from sys import stdin,stdout
	#import numpy as np
	n,k=map(int,stdin.readline().split())
	a=tuple(map(int,stdin.readline().split()))
	minim=min(a)
	maxim=max(a)
	arr=list(a)	
	for i in range(n):
		arr[i]-=minim
	if max(arr) > k:
		stdout.write('NO')
	else:
		stdout.write('YES\n')
		for i in a:
			stdout.write('1 '*minim)
			for j in range(i-minim):
				stdout.write(str(j%k+1)+' ')
			stdout.write('\n')
if __name__=='__main__':
	main()
'''
'''
def main():
	from sys import stdin,stdout
	n,p=[],[]
	for _ in range(int(stdin.readline())):
		last=int(stdin.readline())
		if last<0:
			n.append(-1*last)
		else:
			p.append(last)
	if sum(p)>sum(n):
		stdout.write('first')
	elif sum(n)>sum(p):
		stdout.write('second')
	else:
		maxim=max(n,p)
		#print(maxim)
		if maxim==p:
			if maxim==n:
				if last<0:
					stdout.write('second')
				else:
					stdout.write('first')
			else:
				stdout.write('first')
		else:
			stdout.write('second')
		
if __name__=='__main__':
	main()
'''
#286C
'''
def main():
	from sys import stdin,stdout
	m,n=map(int,stdin.readline().split())
	minim=min(m,n)
	stdout.write(str(minim+1)+'\n')
	if n==minim:
		for i in range(minim+1):
			stdout.write(str(m)+' '+str(i)+'\n')
			m-=1
	else:
		for i in range(minim+1):
			stdout.write(str(i)+' '+str(n)+'\n')
			n-=1
if __name__=='__main__':
	main()
'''
#387B
'''
def main():
	from sys import stdin,stdout
	n,m=map(int,stdin.readline().split())
	a=tuple(map(int,stdin.readline().split()))
	b=tuple(map(int,stdin.readline().split()))
	i=0
	j=0
	while True:
		#print(i,j)
		if i>=n or j>=m:
			break
		if b[j]>=a[i]:
			i+=1
			j+=1
		else:
			j+=1
	stdout.write(str(n-i))
if __name__=='__main__':
	main()
'''
#365B
'''
def main():
	from sys import stdin,stdout
	n=int(stdin.readline())
	a=tuple(map(int,stdin.readline().split()))
	maxim=2
	count=2
	i=2
	while True:
		if i>=n:
			break
		if a[i]==a[i-1]+a[i-2]:
			count+=1
			maxim=max(count,maxim)
		else:
			count=2
		i+=1
	stdout.write(str(min(maxim,n)))
if __name__=='__main__':
	main()
'''	
#431C
#not working
'''
def power(a,b):
	if b:
		if b &1:
			return a*power(a,b-1)
		else:
			return power(a*a,b//2)
	else:
		return 1
def main():
	from sys import stdin,stdout
	import math
	#print(power(2,10))
	n,k,d=map(int,stdin.readline().split())
	layers=n-(d-1)
	size=(power(k,layers)-1)//(k-1)
	size*=k
	arr=[0]
	for i in range(1,size+1):
		if i % k:
			arr.append(arr[math.ceil(i/k)-1]+i%k)
		else:
			arr.append(arr[math.ceil(i/k)-1]+k)
	stdout.write(str(arr.count(n)))	
if __name__=='__main__':
	main()
'''
#157B
def main():
	from sys import stdin,stdout
	import math
	n=int(stdin.readline())
	l=sorted(map(int,stdin.readline().split()))
	if n & 1:
		l=[0]+l
	area=0
	for i in range(0,n,2):
		area+=l[i+1]*l[i+1]-l[i]*l[i]
	stdout.write(str(area*math.pi))
if __name__=='__main__':
	main()
#474D
'''
def main():
	from sys import stdin,stdout
	MOD=int(1e9)+7
	t,k=map(int,stdin.readline().split())
	fib=[1 for i in range(k)]
	for i in range(k,100001):
		fib.append((fib[i-1]%MOD+fib[i-k]%MOD)%MOD)
	for _ in range(t):
		a,b=map(int,stdin.readline().split())
		total=0
		for i in range(a,b+1):
			total=(total+fib[i])%MOD
		stdout.write(str(total)+'\n')
if __name__=='__main__':
	main()
'''