import itertools



N = int(eval(input()))

xy = [[0.0, 0.0]] * N

for i in range(N):

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



def distance(a, b):

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

  return res ** 0.5

  

ans = 0.0

cnt = 0

perms = itertools.permutations(list(range(N)))

for perm in perms:

  cnt += 1

  for j in range(N-1):

    a = perm[j]

    b = perm[j+1]

    ans += distance(xy[a], xy[b])



ans /= cnt

print(ans)

import itertools



N = int(eval(input()))

xy = [[0.0, 0.0]] * N

for i in range(N):

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



def distance(a, b):

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

  return res ** 0.5

  

ans = 0.0

combs = itertools.combinations(list(range(N)), 2)

for comb in combs:

  ans += distance(xy[comb[0]], xy[comb[1]])



ans = ans * 2 / N

print(ans)

import itertools

N = int(eval(input()))
xy = [[0.0, 0.0]] * N
for i in range(N):
    xy[i] = list(map(int, input().split()))


def distance(a, b):
    res = (a[0] - b[0]) ** 2 + (a[1] - b[1]) ** 2
    return res**0.5


ans = 0.0
cnt = 0
perms = itertools.permutations(list(range(N)))
for perm in perms:
    cnt += 1
    for j in range(N - 1):
        a = perm[j]
        b = perm[j + 1]
        ans += distance(xy[a], xy[b])
ans /= cnt
print(ans)

import itertools

N = int(eval(input()))
xy = [[0.0, 0.0]] * N
for i in range(N):
    xy[i] = list(map(int, input().split()))


def distance(a, b):
    res = (a[0] - b[0]) ** 2 + (a[1] - b[1]) ** 2
    return res**0.5


ans = 0.0
combs = itertools.combinations(list(range(N)), 2)
for comb in combs:
    ans += distance(xy[comb[0]], xy[comb[1]])
ans = ans * 2 / N
print(ans)

-cnt = 0 -perms = itertools.permutations(list(range(N))) -for perm in perms: -    cnt += 1 -    for j in range(N - 1): -        a = perm[j] -        b = perm[j + 1] -        ans += distance(xy[a], xy[b]) -ans /= cnt +combs = itertools.combinations(list(range(N)), 2) +for comb in combs: +    ans += distance(xy[comb[0]], xy[comb[1]]) +ans = ans * 2 / N