from itertools import permutations

import math

def dist(x,y):

    return ((x[0]-y[0])**2+(x[1]-y[1])**2)**(0.5)

N = int(eval(input()))

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

ans = 0

for z in permutations(list(range(N)),N):

    for i in range(N-1):

        ans += dist(X[z[i]],X[z[(i+1)%N]])

print((ans/math.factorial(N)))
from itertools import permutations

def dist(x,y):

    return ((x[0]-y[0])**2+(x[1]-y[1])**2)**0.5

N = int(eval(input()))

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

tot = 0

cnt = 0

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

    cnt += 1

    for i in range(1,N):

        tot += dist(X[z[i]],X[z[i-1]])

print((tot/cnt))
from itertools import permutations
import math


def dist(x, y):
    return ((x[0] - y[0]) ** 2 + (x[1] - y[1]) ** 2) ** (0.5)


N = int(eval(input()))
X = [list(map(int, input().split())) for _ in range(N)]
ans = 0
for z in permutations(list(range(N)), N):
    for i in range(N - 1):
        ans += dist(X[z[i]], X[z[(i + 1) % N]])
print((ans / math.factorial(N)))

from itertools import permutations


def dist(x, y):
    return ((x[0] - y[0]) ** 2 + (x[1] - y[1]) ** 2) ** 0.5


N = int(eval(input()))
X = [list(map(int, input().split())) for _ in range(N)]
tot = 0
cnt = 0
for z in permutations(list(range(N))):
    cnt += 1
    for i in range(1, N):
        tot += dist(X[z[i]], X[z[i - 1]])
print((tot / cnt))

-import math -    return ((x[0] - y[0]) ** 2 + (x[1] - y[1]) ** 2) ** (0.5) +    return ((x[0] - y[0]) ** 2 + (x[1] - y[1]) ** 2) ** 0.5 -ans = 0 -for z in permutations(list(range(N)), N): -    for i in range(N - 1): -        ans += dist(X[z[i]], X[z[(i + 1) % N]]) -print((ans / math.factorial(N))) +tot = 0 +cnt = 0 +for z in permutations(list(range(N))): +    cnt += 1 +    for i in range(1, N): +        tot += dist(X[z[i]], X[z[i - 1]]) +print((tot / cnt))