import itertools



N = int(eval(input()))

P = []

L_total = []

for i in range(N):

    p = list(map(int, input().split()))

    P.append(p)

for v in itertools.permutations(P, N):

    L = []

    for i in range(N - 1):

        l = ((v[i][0] - v[i + 1][0]) ** 2 + (v[i][1] - v[i + 1][1]) ** 2) ** 0.5

        L.append(l)

    L_total.append(sum(L))

ans = sum(L_total) / (len(L_total))

print(ans)
from itertools import permutations

import math



n = int(eval(input()))

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

total = 0

for v in permutations(arr, n):

    d = 0

    for i in range(n-1):

        x1, y1 = v[i]

        x2, y2 = v[i+1]

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

    total += d

print((total / math.factorial(n)))



import itertools

N = int(eval(input()))
P = []
L_total = []
for i in range(N):
    p = list(map(int, input().split()))
    P.append(p)
for v in itertools.permutations(P, N):
    L = []
    for i in range(N - 1):
        l = ((v[i][0] - v[i + 1][0]) ** 2 + (v[i][1] - v[i + 1][1]) ** 2) ** 0.5
        L.append(l)
    L_total.append(sum(L))
ans = sum(L_total) / (len(L_total))
print(ans)

from itertools import permutations
import math

n = int(eval(input()))
arr = [tuple(map(int, input().split())) for _ in range(n)]
total = 0
for v in permutations(arr, n):
    d = 0
    for i in range(n - 1):
        x1, y1 = v[i]
        x2, y2 = v[i + 1]
        d += math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2)
    total += d
print((total / math.factorial(n)))

-import itertools +from itertools import permutations +import math -N = int(eval(input())) -P = [] -L_total = [] -for i in range(N): -    p = list(map(int, input().split())) -    P.append(p) -for v in itertools.permutations(P, N): -    L = [] -    for i in range(N - 1): -        l = ((v[i][0] - v[i + 1][0]) ** 2 + (v[i][1] - v[i + 1][1]) ** 2) ** 0.5 -        L.append(l) -    L_total.append(sum(L)) -ans = sum(L_total) / (len(L_total)) -print(ans) +n = int(eval(input())) +arr = [tuple(map(int, input().split())) for _ in range(n)] +total = 0 +for v in permutations(arr, n): +    d = 0 +    for i in range(n - 1): +        x1, y1 = v[i] +        x2, y2 = v[i + 1] +        d += math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2) +    total += d +print((total / math.factorial(n)))