from itertools import permutations

n = int(eval(input()))

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

N = list(range(n))



ans = 0

cnt = 0

for v in permutations(N):

    x = 0

    for i in range(n-1):

        a = v[i]

        b = v[i+1]

        x += ((xy[a][0]-xy[b][0])**2 + (xy[a][1]-xy[b][1])**2) ** 0.5

    cnt += 1

    ans += x

print((ans/cnt))
import itertools

n = int(eval(input()))

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



ans = []

X = 0

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

  cnt = 0

  X += 1

  for i in range(n-1):

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

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

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

  ans.append(cnt)

print((sum(ans)/X))
from itertools import permutations

n = int(eval(input()))
xy = [list(map(int, input().split())) for _ in range(n)]
N = list(range(n))
ans = 0
cnt = 0
for v in permutations(N):
    x = 0
    for i in range(n - 1):
        a = v[i]
        b = v[i + 1]
        x += ((xy[a][0] - xy[b][0]) ** 2 + (xy[a][1] - xy[b][1]) ** 2) ** 0.5
    cnt += 1
    ans += x
print((ans / cnt))

import itertools

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

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