import math

import itertools



n = int(eval(input()))

xy = [ list(map(int, input().split())) for _ in range(n) ]

p = itertools.permutations(xy, n)

c = 0

for i in p:

  for j in range(n-1):

    c += ( (i[j][0]-i[j+1][0])**2 + (i[j][1]-i[j+1][1])**2 )**0.5

    

l = math.factorial(n)

print((c/l))
from itertools import permutations

from math import factorial

def d(a, b):

  x1, y1 = a

  x2, y2 = b

  return ((x1-x2)**2 + (y1-y2)**2)**0.5



cnt = 0

n = int(eval(input()))

XY = [list(map(int, input().split())) for _ in range(n)]

for l in permutations(XY):

  for i in range(n-1):

    cnt += d(l[i], l[i+1])

cnt /= factorial(n)

print(cnt)
import math
import itertools

n = int(eval(input()))
xy = [list(map(int, input().split())) for _ in range(n)]
p = itertools.permutations(xy, n)
c = 0
for i in p:
    for j in range(n - 1):
        c += ((i[j][0] - i[j + 1][0]) ** 2 + (i[j][1] - i[j + 1][1]) ** 2) ** 0.5
l = math.factorial(n)
print((c / l))

from itertools import permutations
from math import factorial


def d(a, b):
    x1, y1 = a
    x2, y2 = b
    return ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5


cnt = 0
n = int(eval(input()))
XY = [list(map(int, input().split())) for _ in range(n)]
for l in permutations(XY):
    for i in range(n - 1):
        cnt += d(l[i], l[i + 1])
cnt /= factorial(n)
print(cnt)

-import math -import itertools +from itertools import permutations +from math import factorial + +def d(a, b): +    x1, y1 = a +    x2, y2 = b +    return ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5 + + +cnt = 0 -xy = [list(map(int, input().split())) for _ in range(n)] -p = itertools.permutations(xy, n) -c = 0 -for i in p: -    for j in range(n - 1): -        c += ((i[j][0] - i[j + 1][0]) ** 2 + (i[j][1] - i[j + 1][1]) ** 2) ** 0.5 -l = math.factorial(n) -print((c / l)) +XY = [list(map(int, input().split())) for _ in range(n)] +for l in permutations(XY): +    for i in range(n - 1): +        cnt += d(l[i], l[i + 1]) +cnt /= factorial(n) +print(cnt)