import itertools

n = int(eval(input()))

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



ans = []

for v in itertools.permutations(list(range(n)), n):

    a = 0

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

        x1,y1 = xy[v[i]][0], xy[v[i]][1]

        x2,y2 = xy[v[i+1]][0], xy[v[i+1]][1]

        a += ((x1-x2)**2+(y1-y2)**2)**0.5

    ans.append(a)

print((sum(ans)/len(ans)))
import itertools

from math import sqrt

n = int(eval(input()))

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

ans = 0

cnt = 0

for v in itertools.permutations(list(range(n))):

    for i in range(n-1):

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

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

        ans += sqrt(x+y)

    cnt += 1

print((ans/cnt))
import itertools

n = int(eval(input()))
xy = [list(map(int, input().split())) for _ in range(n)]
ans = []
for v in itertools.permutations(list(range(n)), n):
    a = 0
    for i in range(len(v) - 1):
        x1, y1 = xy[v[i]][0], xy[v[i]][1]
        x2, y2 = xy[v[i + 1]][0], xy[v[i + 1]][1]
        a += ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5
    ans.append(a)
print((sum(ans) / len(ans)))

import itertools
from math import sqrt

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

+from math import sqrt -ans = [] -for v in itertools.permutations(list(range(n)), n): -    a = 0 -    for i in range(len(v) - 1): -        x1, y1 = xy[v[i]][0], xy[v[i]][1] -        x2, y2 = xy[v[i + 1]][0], xy[v[i + 1]][1] -        a += ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5 -    ans.append(a) -print((sum(ans) / len(ans))) +ans = 0 +cnt = 0 +for v in itertools.permutations(list(range(n))): +    for i in range(n - 1): +        x = (xy[v[i]][0] - xy[v[i + 1]][0]) ** 2 +        y = (xy[v[i]][1] - xy[v[i + 1]][1]) ** 2 +        ans += sqrt(x + y) +    cnt += 1 +print((ans / cnt))