import math

import itertools

N = int(eval(input()))

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



all_root = list(itertools.permutations(xy))



ret = 0

for root in all_root:

    for i in range(len(root)-1):

        x = (root[i][0] - root[i+1][0]) ** 2

        y = (root[i][1] - root[i+1][1]) ** 2

        ret += math.sqrt(x+y)



print((ret/len(all_root)))
import math

from itertools import permutations



N = int(eval(input()))

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



ret = 0

cnt = 0

for i in permutations(xy):

    for j in range(N-1):

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

        y = (i[j][1] - i[j+1][1]) ** 2

        ret += math.sqrt(x+y)

    cnt += 1

print((ret/cnt))



import math
import itertools

N = int(eval(input()))
xy = [list(map(int, input().split())) for _ in range(N)]
all_root = list(itertools.permutations(xy))
ret = 0
for root in all_root:
    for i in range(len(root) - 1):
        x = (root[i][0] - root[i + 1][0]) ** 2
        y = (root[i][1] - root[i + 1][1]) ** 2
        ret += math.sqrt(x + y)
print((ret / len(all_root)))

import math
from itertools import permutations

N = int(eval(input()))
xy = [list(map(int, input().split())) for _ in range(N)]
ret = 0
cnt = 0
for i in permutations(xy):
    for j in range(N - 1):
        x = (i[j][0] - i[j + 1][0]) ** 2
        y = (i[j][1] - i[j + 1][1]) ** 2
        ret += math.sqrt(x + y)
    cnt += 1
print((ret / cnt))

-import itertools +from itertools import permutations -all_root = list(itertools.permutations(xy)) -for root in all_root: -    for i in range(len(root) - 1): -        x = (root[i][0] - root[i + 1][0]) ** 2 -        y = (root[i][1] - root[i + 1][1]) ** 2 +cnt = 0 +for i in permutations(xy): +    for j in range(N - 1): +        x = (i[j][0] - i[j + 1][0]) ** 2 +        y = (i[j][1] - i[j + 1][1]) ** 2 -print((ret / len(all_root))) +    cnt += 1 +print((ret / cnt))