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:
#!/usr/bin/env python
from __future__ import division, print_function
import math
import os
import sys
from sys import stdin,stdout
from io import BytesIO, IOBase
from itertools import accumulate
from collections import deque
#sys.setrecursionlimit(10**5)
if sys.version_info[0] < 3:
    from __builtin__ import xrange as range
    from future_builtins import ascii, filter, hex, map, oct, zip


# region fastio

BUFSIZE = 8192


class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()

    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")


def print(*args, **kwargs):
    """Prints the values to a stream, or to sys.stdout by default."""
    sep, file = kwargs.pop("sep", " "), kwargs.pop("file", sys.stdout)
    at_start = True
    for x in args:
        if not at_start:
            file.write(sep)
        file.write(str(x))
        at_start = False
    file.write(kwargs.pop("end", "\n"))
    if kwargs.pop("flush", False):
        file.flush()


if sys.version_info[0] < 3:
    sys.stdin, sys.stdout = FastIO(sys.stdin), FastIO(sys.stdout)
else:
    sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)

input = lambda: sys.stdin.readline().rstrip("\r\n")
#-----------------------------------------------------------------

def regularbracket(t):
    p=0
    for i in t:
        if i=="(":
            p+=1
        else:
            p-=1
        if p<0:
            return False
    else:
        if p>0:
            return False
        else:
            return True

#-------------------------------------------------
def binarySearchCount(arr, n, key):
    left = 0
    right = n - 1

    count = 0

    while (left <= right):
        mid = int((right + left) / 2)

        # Check if middle element is
        # less than or equal to key
        if (arr[mid] <= key):
            count = mid+1
            left = mid + 1

        # If key is smaller, ignore right half
        else:
            right = mid - 1
    return count
#------------------------------reverse string(pallindrome)
def reverse1(string):
    pp=""
    for i in string[::-1]:
        pp+=i
    if pp==string:
        return True
    return False
#--------------------------------reverse list(paindrome)
def reverse2(list1):
    l=[]
    for i in list1[::-1]:
        l.append(i)
    if l==list1:
        return True
    return False
# endregion
import math
def mex(list1):
    #list1 = sorted(list1)
    p = max(list1)+1
    for i in range(len(list1)):
        if list1[i]!=i:
            p = i
            break
    return p
#----endregion
"""
def main():
    n,m = map(int,input().split())
    np = list(map(int,input().split()))
    mp = list(map(int,input().split()))
    np = sorted(np)
    mp = sorted(mp)
    cnt=0
    for i in np:
        if len(mp)==0:
            cnt+=1
        elif i in mp:
            continue
        elif i>max(mp):
            cnt+=1
        elif i<max(mp):
            #cnt-=1
            for j in mp:
                if j>i:
                    mp.remove(j)
                    break
    print(cnt)
"""
"""
def main():
    n = int(input())
    arr = list(map(int,input().split()))
    max=0
    if len(arr)==1:
        print(1)
    elif len(arr)==2:
        print(2)
    else:
        cnt=2
        for i in range(n-2):
            if arr[i+2]==arr[i+1]+arr[i]:
                cnt+=1
            else:
                if cnt>max:
                    max = cnt

                cnt=2
        if cnt>max:
            max=cnt
        print(max)
"""
def main():
    n = int(input())
    arr = list(map(int,input().split()))
    arr = sorted(arr)
    p=0
    if len(arr)%2!=0:
        c = (math.pi)*(pow(arr[0],2))
        arr.pop(0)
        i=0
        p=0
        while(i<len(arr)-1):
            p+=(math.pi*(pow(arr[i+1],2))) - ((math.pi*(pow(arr[i],2))))
            i+=2
        print(p+c)
    else:
        i=0
        while(i<len(arr)-1):
            p += (math.pi * (pow(arr[i + 1], 2))) - ((math.pi * (pow(arr[i], 2))))
            i+=2
        print(p)
if __name__ == '__main__':
    main()