from itertools import permutations

from itertools import combinations

from math import sqrt

from math import factorial

from collections import defaultdict



N = int(eval(input()))



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



length = defaultdict(float)

l_sum = 0

res = 0



for a, b in combinations(list(range(N)),2):

    length[(a, b)] = (sqrt( (points[a][0] - points[b][0])**2 + (points[a][1] - points[b][1])**2 ))



for a in permutations(list(range(N))):

    for i in range(N-1):

        l_sum += length[(min(a[i], a[i+1]), max(a[i], a[i+1]))]



res = l_sum/factorial(N)



print(res)
from itertools import permutations

from math import factorial

N = int(eval(input()))

data = []

for _ in range(N):

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

    data.append((x,y))

res = 0

for a in permutations(data,N):

    x0, y0 = a[0]

    for x, y in a[1:]:

        res += ((x-x0)**2 + (y-y0)**2)**(0.5)

        x0, y0 = x, y



print((res/factorial(N)))
from itertools import permutations
from itertools import combinations
from math import sqrt
from math import factorial
from collections import defaultdict

N = int(eval(input()))
points = [list(map(int, input().split())) for _ in range(N)]
length = defaultdict(float)
l_sum = 0
res = 0
for a, b in combinations(list(range(N)), 2):
    length[(a, b)] = sqrt(
        (points[a][0] - points[b][0]) ** 2 + (points[a][1] - points[b][1]) ** 2
    )
for a in permutations(list(range(N))):
    for i in range(N - 1):
        l_sum += length[(min(a[i], a[i + 1]), max(a[i], a[i + 1]))]
res = l_sum / factorial(N)
print(res)

from itertools import permutations
from math import factorial

N = int(eval(input()))
data = []
for _ in range(N):
    x, y = list(map(int, input().split()))
    data.append((x, y))
res = 0
for a in permutations(data, N):
    x0, y0 = a[0]
    for x, y in a[1:]:
        res += ((x - x0) ** 2 + (y - y0) ** 2) ** (0.5)
        x0, y0 = x, y
print((res / factorial(N)))

-from itertools import combinations -from math import sqrt -from collections import defaultdict -points = [list(map(int, input().split())) for _ in range(N)] -length = defaultdict(float) -l_sum = 0 +data = [] +for _ in range(N): +    x, y = list(map(int, input().split())) +    data.append((x, y)) -for a, b in combinations(list(range(N)), 2): -    length[(a, b)] = sqrt( -        (points[a][0] - points[b][0]) ** 2 + (points[a][1] - points[b][1]) ** 2 -    ) -for a in permutations(list(range(N))): -    for i in range(N - 1): -        l_sum += length[(min(a[i], a[i + 1]), max(a[i], a[i + 1]))] -res = l_sum / factorial(N) -print(res) +for a in permutations(data, N): +    x0, y0 = a[0] +    for x, y in a[1:]: +        res += ((x - x0) ** 2 + (y - y0) ** 2) ** (0.5) +        x0, y0 = x, y +print((res / factorial(N)))