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 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 cmb in itertools.combinations(C, 2):

    s += 2 * dist(cmb[0], cmb[1]) / N



print(s)

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 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 cmb in itertools.combinations(C, 2):
    s += 2 * dist(cmb[0], cmb[1]) / N
print(s)

-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))))) +for cmb in itertools.combinations(C, 2): +    s += 2 * dist(cmb[0], cmb[1]) / N +print(s)