n=int(eval(input()))

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



import itertools

import math

temp=[i for i in range(n)]

perm=list(itertools.permutations(temp))



sm=0

count=0

for route in perm:

    count+=1

    temp_dis=0

    route_list=list(route)

    for i in range(1,n):

        j=route_list[i]

        k=route_list[i-1]

        temp_dis+=math.sqrt((distance[j][0]-distance[k][0])**2+(distance[j][1]-distance[k][1])**2)

    sm+=temp_dis

ans=sm/count

print(('{:.9f}'.format(ans)))

import math

import itertools

n = int(eval(input()))

#n, m = map(int, input().split())

#hl = list(map(int, input().split()))

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

total = 0

townnum = [i for i in range(n)]

for v in itertools.permutations(townnum):

    for j in range(1, n):

        cur = l[v[j]]

        bef = l[v[j-1]]

        total += math.sqrt((cur[0]-bef[0])**2+(cur[1]-bef[1])**2)

ans = total/math.factorial(n)

print(('{:.9f}'.format(ans)))
n = int(eval(input()))
distance = [list(map(int, input().split())) for i in range(n)]
import itertools
import math

temp = [i for i in range(n)]
perm = list(itertools.permutations(temp))
sm = 0
count = 0
for route in perm:
    count += 1
    temp_dis = 0
    route_list = list(route)
    for i in range(1, n):
        j = route_list[i]
        k = route_list[i - 1]
        temp_dis += math.sqrt(
            (distance[j][0] - distance[k][0]) ** 2
            + (distance[j][1] - distance[k][1]) ** 2
        )
    sm += temp_dis
ans = sm / count
print(("{:.9f}".format(ans)))

import math
import itertools

n = int(eval(input()))
# n, m = map(int, input().split())
# hl = list(map(int, input().split()))
l = [list(map(int, input().split())) for i in range(n)]
total = 0
townnum = [i for i in range(n)]
for v in itertools.permutations(townnum):
    for j in range(1, n):
        cur = l[v[j]]
        bef = l[v[j - 1]]
        total += math.sqrt((cur[0] - bef[0]) ** 2 + (cur[1] - bef[1]) ** 2)
ans = total / math.factorial(n)
print(("{:.9f}".format(ans)))

+import math +import itertools + -distance = [list(map(int, input().split())) for i in range(n)] -import itertools -import math - -temp = [i for i in range(n)] -perm = list(itertools.permutations(temp)) -sm = 0 -count = 0 -for route in perm: -    count += 1 -    temp_dis = 0 -    route_list = list(route) -    for i in range(1, n): -        j = route_list[i] -        k = route_list[i - 1] -        temp_dis += math.sqrt( -            (distance[j][0] - distance[k][0]) ** 2 -            + (distance[j][1] - distance[k][1]) ** 2 -        ) -    sm += temp_dis -ans = sm / count +# n, m = map(int, input().split()) +# hl = list(map(int, input().split())) +l = [list(map(int, input().split())) for i in range(n)] +total = 0 +townnum = [i for i in range(n)] +for v in itertools.permutations(townnum): +    for j in range(1, n): +        cur = l[v[j]] +        bef = l[v[j - 1]] +        total += math.sqrt((cur[0] - bef[0]) ** 2 + (cur[1] - bef[1]) ** 2) +ans = total / math.factorial(n)