#!/usr/bin/env python

import sys

from math import sqrt



def _s(): return sys.stdin.readline().strip()



def _i(): return int(sys.stdin.readline().strip())

def _ia(): return [ int(x) for x in sys.stdin.readline().strip().split() ]



def g(a):

    if len(a)==1:

        yield a

    else:

        for i in range(len(a)):

            ai = a[i]

            for aa in g(a[:i]+a[i+1:]):

                yield [ ai ] + aa

        



n = _i()

xy = [ _ia() for _ in range(n) ]



s = 0

c = 0

for a in g(xy):

    dist = 0

    prev = None

    for nxt in a:

        if prev:

            dist += sqrt( (prev[0]-nxt[0])**2 + (prev[1]-nxt[1])**2 )

        prev = nxt

    s += dist

    c +=1

#

print((s/c))

#!/usr/bin/env python

import sys

from math import sqrt, factorial

from itertools import permutations



def _i(): return int(sys.stdin.readline().strip())

def _ia(): return [int(x) for x in sys.stdin.readline().strip().split()]





n = _i()

xy = [_ia() for _ in range(n)]



tot = 0

for s in permutations([i for i in range(n)]):

    i = s[0]

    tmp = 0

    for j in s[1:]:

        dx = xy[i][0] - xy[j][0]

        dy = xy[i][1] - xy[j][1]

        tmp += sqrt(dx ** 2 + dy ** 2)

        i = j

    tot += tmp



print((tot / factorial(n)))

#!/usr/bin/env python
import sys
from math import sqrt


def _s():
    return sys.stdin.readline().strip()


def _i():
    return int(sys.stdin.readline().strip())


def _ia():
    return [int(x) for x in sys.stdin.readline().strip().split()]


def g(a):
    if len(a) == 1:
        yield a
    else:
        for i in range(len(a)):
            ai = a[i]
            for aa in g(a[:i] + a[i + 1 :]):
                yield [ai] + aa


n = _i()
xy = [_ia() for _ in range(n)]
s = 0
c = 0
for a in g(xy):
    dist = 0
    prev = None
    for nxt in a:
        if prev:
            dist += sqrt((prev[0] - nxt[0]) ** 2 + (prev[1] - nxt[1]) ** 2)
        prev = nxt
    s += dist
    c += 1
#
print((s / c))

#!/usr/bin/env python
import sys
from math import sqrt, factorial
from itertools import permutations


def _i():
    return int(sys.stdin.readline().strip())


def _ia():
    return [int(x) for x in sys.stdin.readline().strip().split()]


n = _i()
xy = [_ia() for _ in range(n)]
tot = 0
for s in permutations([i for i in range(n)]):
    i = s[0]
    tmp = 0
    for j in s[1:]:
        dx = xy[i][0] - xy[j][0]
        dy = xy[i][1] - xy[j][1]
        tmp += sqrt(dx**2 + dy**2)
        i = j
    tot += tmp
print((tot / factorial(n)))

-from math import sqrt - - -def _s(): -    return sys.stdin.readline().strip() +from math import sqrt, factorial +from itertools import permutations -def g(a): -    if len(a) == 1: -        yield a -    else: -        for i in range(len(a)): -            ai = a[i] -            for aa in g(a[:i] + a[i + 1 :]): -                yield [ai] + aa - - -s = 0 -c = 0 -for a in g(xy): -    dist = 0 -    prev = None -    for nxt in a: -        if prev: -            dist += sqrt((prev[0] - nxt[0]) ** 2 + (prev[1] - nxt[1]) ** 2) -        prev = nxt -    s += dist -    c += 1 -# -print((s / c)) +tot = 0 +for s in permutations([i for i in range(n)]): +    i = s[0] +    tmp = 0 +    for j in s[1:]: +        dx = xy[i][0] - xy[j][0] +        dy = xy[i][1] - xy[j][1] +        tmp += sqrt(dx**2 + dy**2) +        i = j +    tot += tmp +print((tot / factorial(n)))