import math

import itertools

n = int(eval(input()))



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



for i in range(n):

    xys[i] = list(map(int,input().split()))





m = math.factorial(n)

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

cs = itertools.permutations(c)



s = 0

for d in cs:

    for j in range(len(d)-1):

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

        s += x ** (0.5)



print((s/m))

import itertools

import math

n = int(eval(input()))



points = []

for i in range(n):

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

    points.append([x,y])





cs = list(itertools.combinations(points,2))

ans = 0

for a,b in cs:

    c = (a[0]-b[0]) ** 2 + (a[1]-b[1]) ** 2

    ans += math.sqrt(c)



ans = (ans / n) * 2

print(ans)

import math
import itertools

n = int(eval(input()))
xys = [[] for i in range(n)]
for i in range(n):
    xys[i] = list(map(int, input().split()))
m = math.factorial(n)
c = [i for i in range(n)]
cs = itertools.permutations(c)
s = 0
for d in cs:
    for j in range(len(d) - 1):
        x = (xys[d[j]][0] - xys[d[j + 1]][0]) ** 2 + (
            xys[d[j]][1] - xys[d[j + 1]][1]
        ) ** 2
        s += x ** (0.5)
print((s / m))

import itertools
import math

n = int(eval(input()))
points = []
for i in range(n):
    x, y = list(map(int, input().split()))
    points.append([x, y])
cs = list(itertools.combinations(points, 2))
ans = 0
for a, b in cs:
    c = (a[0] - b[0]) ** 2 + (a[1] - b[1]) ** 2
    ans += math.sqrt(c)
ans = (ans / n) * 2
print(ans)

+import itertools -import itertools -xys = [[] for i in range(n)] +points = [] -    xys[i] = list(map(int, input().split())) -m = math.factorial(n) -c = [i for i in range(n)] -cs = itertools.permutations(c) -s = 0 -for d in cs: -    for j in range(len(d) - 1): -        x = (xys[d[j]][0] - xys[d[j + 1]][0]) ** 2 + ( -            xys[d[j]][1] - xys[d[j + 1]][1] -        ) ** 2 -        s += x ** (0.5) -print((s / m)) +    x, y = list(map(int, input().split())) +    points.append([x, y]) +cs = list(itertools.combinations(points, 2)) +ans = 0 +for a, b in cs: +    c = (a[0] - b[0]) ** 2 + (a[1] - b[1]) ** 2 +    ans += math.sqrt(c) +ans = (ans / n) * 2 +print(ans)