import itertools

import math

n=int(eval(input()))

lst=[None]*n

for i in range(n):

    lst[i]=tuple(map(int, input().split()))

total=0

for v in itertools.permutations(lst):

    for i in range(n-1):

        dis=math.sqrt( (v[i][0]-v[i+1][0])**2 + (v[i][1]-v[i+1][1])**2 )

        total+=dis

print((total/math.factorial(n)))



import itertools

import math

N=int(eval(input()))

lst=[None]*N

for i in range(N):

    lst[i]=tuple(map(int, input().split()))

total=0

for i in range(N-1):

    for j in range(i+1,N):

        total+=math.sqrt( (lst[i][0]-lst[j][0])**2 + (lst[i][1]-lst[j][1])**2 )



ave=total*2/N

print(ave)
import itertools
import math

n = int(eval(input()))
lst = [None] * n
for i in range(n):
    lst[i] = tuple(map(int, input().split()))
total = 0
for v in itertools.permutations(lst):
    for i in range(n - 1):
        dis = math.sqrt((v[i][0] - v[i + 1][0]) ** 2 + (v[i][1] - v[i + 1][1]) ** 2)
        total += dis
print((total / math.factorial(n)))

import itertools
import math

N = int(eval(input()))
lst = [None] * N
for i in range(N):
    lst[i] = tuple(map(int, input().split()))
total = 0
for i in range(N - 1):
    for j in range(i + 1, N):
        total += math.sqrt((lst[i][0] - lst[j][0]) ** 2 + (lst[i][1] - lst[j][1]) ** 2)
ave = total * 2 / N
print(ave)

-n = int(eval(input())) -lst = [None] * n -for i in range(n): +N = int(eval(input())) +lst = [None] * N +for i in range(N): -for v in itertools.permutations(lst): -    for i in range(n - 1): -        dis = math.sqrt((v[i][0] - v[i + 1][0]) ** 2 + (v[i][1] - v[i + 1][1]) ** 2) -        total += dis -print((total / math.factorial(n))) +for i in range(N - 1): +    for j in range(i + 1, N): +        total += math.sqrt((lst[i][0] - lst[j][0]) ** 2 + (lst[i][1] - lst[j][1]) ** 2) +ave = total * 2 / N +print(ave)