volf52

import operator as op
def ncr(n, x):
    x = min(n, n-x)
    if x == 0: return 1
    num = reduce(op.mul, xrange(n, n-x, -1))
    denom = reduce(op.mul, xrange(1, x+1))
    return num // denom

volf52

from math import erf

def F(x, mew, sd):
    return 0.5 * (1 + erf((x-mew)/(sd * pow(2, 0.5))))

volf52

def hexdump(src, length=16):
    '''
    :param src: https://github.com/ActiveState/code/tree/master/recipes/Python/142812_Hex_dumper/
    
    '''
    FILTER=''.join([(len(repr(chr(x)))==3) and chr(x) or '.' for x in range(256)])
    N=0
    result=''
    while src:
       s,src = src[:length],src[length:]

volf52

import os
import socket

if os.name != "nt":
    import fcntl
    import struct

    def get_interface_ip(ifname):
        s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
        return socket.inet_ntoa(fcntl.ioctl(s.fileno(), 0x8915, struct.pack('256s',

volf52

 def up(inp_str):
     if ' ' in inp_str:
        print "No spaces"
        return
     else:
        return ''.join([chr(ord(x) & 95) for x in inp_str])

volf52

def transpose(matrix):
    return [[row[i] for row in matrix] for i in range(len(matrix[0]))]


# this one is a bit slower
def t2(matrix):
    return map(list, zip(*matrix))

volf52

def ranking(arr):
     cp = []
     for x in arr:
         if cp.count(x) == 0:
             cp.append(x)     
     cp.sort()
     ranks = {x:y for x,y in zip(cp, range(1, len(cp)+1))}
     return [ranks[x] for x in arr]

volf52

def main():
    n = int(raw_input().strip())
    X = map(float, raw_input().strip().split(' '))
    Y = map(float, raw_input().strip().split(' '))
    x_rank = ranking(X)
    y_rank = ranking(Y)
    d_sq = [(x-y)**2 for x,y in zip(x_rank, y_rank)]
    print round(1-((6.0*sum(d_sq))/(n*(n**2 - 1))), 3)

volf52

def main():
    n = int(raw_input().strip())
    X = map(float, raw_input().strip().split(' '))
    Y = map(float, raw_input().strip().split(' '))
    x_mean = sum(X) / len(X)
    y_mean = sum(Y) / len(Y)
    s_devX = std(X, x_mean)
    s_devY = std(Y, y_mean)
    covariance = cov(X, Y, x_mean, y_mean)
    print round(covariance / (s_devX * s_devY), 3)

volf52

n = 5 # take input for total lines
X = []
Y = []

for _ in xrange(n):
    x,y = map(int, raw_input().strip().split(' '))
    X.append(x)
    Y.append(y)
# input is done
x_sum = sum(X)