import itertools

import math

N = int(eval(input()))

city_list = []

for i in range(N):

    x, y = [int(z) for z in input().split()]

    city_list.append((x, y))

root_list = list(itertools.permutations(city_list, N))

ave = 0

for root in root_list:

    length = 0

    while len(root) > 1:

        x1, y1, x2, y2 = root[0][0], root[0][1], root[1][0], root[1][1]

        length += math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2)

        root = root[1:]

    ave += (length / len(root_list))

print(ave)

import math

N = int(eval(input()))

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

average = 0

for x1, y1 in city_list:

    for x2, y2 in city_list:

        average += math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2)

print((average / N))

import itertools
import math

N = int(eval(input()))
city_list = []
for i in range(N):
    x, y = [int(z) for z in input().split()]
    city_list.append((x, y))
root_list = list(itertools.permutations(city_list, N))
ave = 0
for root in root_list:
    length = 0
    while len(root) > 1:
        x1, y1, x2, y2 = root[0][0], root[0][1], root[1][0], root[1][1]
        length += math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2)
        root = root[1:]
    ave += length / len(root_list)
print(ave)

import math

N = int(eval(input()))
city_list = [list(map(int, input().split())) for _ in range(N)]
average = 0
for x1, y1 in city_list:
    for x2, y2 in city_list:
        average += math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2)
print((average / N))

-import itertools -city_list = [] -for i in range(N): -    x, y = [int(z) for z in input().split()] -    city_list.append((x, y)) -root_list = list(itertools.permutations(city_list, N)) -ave = 0 -for root in root_list: -    length = 0 -    while len(root) > 1: -        x1, y1, x2, y2 = root[0][0], root[0][1], root[1][0], root[1][1] -        length += math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2) -        root = root[1:] -    ave += length / len(root_list) -print(ave) +city_list = [list(map(int, input().split())) for _ in range(N)] +average = 0 +for x1, y1 in city_list: +    for x2, y2 in city_list: +        average += math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2) +print((average / N))