import itertools,math

def dist(x,y):

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

n = int(eval(input()))

data = [list(map(int,input().split()))for i in range(n)]

ans = 0

for v in itertools.permutations(data):

    for i in range(1,n):

        ans += dist(v[i],v[i-1])



print((ans/math.factorial(n)))
from math import sqrt

from itertools import permutations

def dist(a,b):

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

n = int(eval(input()))

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



ans = 0

for q in permutations(data):

    for i in range(1,n):

        ans += dist(q[i-1],q[i])

for i in range(n):

    ans /= (i+1)

print(ans)
import itertools, math


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


n = int(eval(input()))
data = [list(map(int, input().split())) for i in range(n)]
ans = 0
for v in itertools.permutations(data):
    for i in range(1, n):
        ans += dist(v[i], v[i - 1])
print((ans / math.factorial(n)))

from math import sqrt
from itertools import permutations


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


n = int(eval(input()))
data = [list(map(int, input().split())) for _ in range(n)]
ans = 0
for q in permutations(data):
    for i in range(1, n):
        ans += dist(q[i - 1], q[i])
for i in range(n):
    ans /= i + 1
print(ans)

-import itertools, math +from math import sqrt +from itertools import permutations -def dist(x, y): -    return ((x[0] - y[0]) ** 2 + (x[1] - y[1]) ** 2) ** (1 / 2) +def dist(a, b): +    return sqrt((a[0] - b[0]) ** 2 + (a[1] - b[1]) ** 2) -data = [list(map(int, input().split())) for i in range(n)] +data = [list(map(int, input().split())) for _ in range(n)] -for v in itertools.permutations(data): +for q in permutations(data): -        ans += dist(v[i], v[i - 1]) -print((ans / math.factorial(n))) +        ans += dist(q[i - 1], q[i]) +for i in range(n): +    ans /= i + 1 +print(ans)