import math

import itertools





def dist(a, b):

    return math.sqrt((a[0]-b[0])**2 + (a[1] - b[1])**2)





def length(P, p):

    total = 0

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

        total += dist(P[p[i]], P[p[i+1]])

    return total





N = int(eval(input()))

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



print((sum([length(P, p)

           for p in itertools.permutations(list(range(N)))]) / math.factorial(N)))

import itertools

import math





def dist(a, b):

    return math.sqrt((a[0] - b[0])**2 + (a[1] - b[1])**2)





N = int(eval(input()))

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



s = 0

for per in itertools.permutations(C):

    for i in range(N-1):

        s += dist(per[i], per[i+1])



print((s / len(list(itertools.permutations(C)))))

import math
import itertools


def dist(a, b):
    return math.sqrt((a[0] - b[0]) ** 2 + (a[1] - b[1]) ** 2)


def length(P, p):
    total = 0
    for i in range(len(p) - 1):
        total += dist(P[p[i]], P[p[i + 1]])
    return total


N = int(eval(input()))
P = [list(map(int, input().split())) for _ in range(N)]
print(
    (
        sum([length(P, p) for p in itertools.permutations(list(range(N)))])
        / math.factorial(N)
    )
)

import itertools
import math


def dist(a, b):
    return math.sqrt((a[0] - b[0]) ** 2 + (a[1] - b[1]) ** 2)


N = int(eval(input()))
C = [tuple(map(int, input().split())) for _ in range(N)]
s = 0
for per in itertools.permutations(C):
    for i in range(N - 1):
        s += dist(per[i], per[i + 1])
print((s / len(list(itertools.permutations(C)))))

+import itertools -import itertools -def length(P, p): -    total = 0 -    for i in range(len(p) - 1): -        total += dist(P[p[i]], P[p[i + 1]]) -    return total - - -P = [list(map(int, input().split())) for _ in range(N)] -print( -    ( -        sum([length(P, p) for p in itertools.permutations(list(range(N)))]) -        / math.factorial(N) -    ) -) +C = [tuple(map(int, input().split())) for _ in range(N)] +s = 0 +for per in itertools.permutations(C): +    for i in range(N - 1): +        s += dist(per[i], per[i + 1]) +print((s / len(list(itertools.permutations(C)))))