import numpy as np

from itertools import permutations

from math import hypot



n = int(eval(input()))

cnt = 0

dis = 0



li = []

for _ in range(n):

    i, j = list(map(int, input().split()))

    li.append(np.array([i, j]))



ptn = list(range(n))



for a in permutations(ptn):

    cnt += 1

    for i, j in zip(a,a[1:]):

        x1, y1 = li[i]

        x2, y2 = li[j]

        dis += hypot(x1-x2, y1-y2)



print((dis/cnt))
from itertools import permutations

from math import hypot



n = int(eval(input()))

cnt = 0

dis = 0



li = []

for i in range(n):

    x,y = list(map(int,input().split()))

    li.append([x, y])



ptn = list(range(n))



for a in permutations(ptn):

    cnt += 1

    for i, j in zip(a,a[1:]):

        x1, y1 = li[i]

        x2, y2 = li[j]

        dis += hypot(x1-x2, y1-y2)



print((dis/cnt))
import numpy as np
from itertools import permutations
from math import hypot

n = int(eval(input()))
cnt = 0
dis = 0
li = []
for _ in range(n):
    i, j = list(map(int, input().split()))
    li.append(np.array([i, j]))
ptn = list(range(n))
for a in permutations(ptn):
    cnt += 1
    for i, j in zip(a, a[1:]):
        x1, y1 = li[i]
        x2, y2 = li[j]
        dis += hypot(x1 - x2, y1 - y2)
print((dis / cnt))

from itertools import permutations
from math import hypot

n = int(eval(input()))
cnt = 0
dis = 0
li = []
for i in range(n):
    x, y = list(map(int, input().split()))
    li.append([x, y])
ptn = list(range(n))
for a in permutations(ptn):
    cnt += 1
    for i, j in zip(a, a[1:]):
        x1, y1 = li[i]
        x2, y2 = li[j]
        dis += hypot(x1 - x2, y1 - y2)
print((dis / cnt))

-import numpy as np -for _ in range(n): -    i, j = list(map(int, input().split())) -    li.append(np.array([i, j])) +for i in range(n): +    x, y = list(map(int, input().split())) +    li.append([x, y])