from itertools import permutations

from math import factorial



n = int(eval(input()))

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



root = list(permutations(xy,n))



ans = 0

for r in root:

    a = 0

    for i in range(n-1):

        a += ((r[i+1][0]-r[i][0])**2 + (r[i+1][1]-r[i][1])**2)**0.5

    ans += a

print((ans/factorial(n)))

from itertools import combinations

n = int(eval(input()))

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



pair = list(combinations(xy,2))



ans = 0

for p in pair:

    ans += ((p[0][0]-p[1][0])**2 + (p[0][1]-p[1][1])**2)**0.5

print((ans*(n-1)/len(pair)))

from itertools import permutations
from math import factorial

n = int(eval(input()))
xy = [list(map(int, input().split())) for i in range(n)]
root = list(permutations(xy, n))
ans = 0
for r in root:
    a = 0
    for i in range(n - 1):
        a += ((r[i + 1][0] - r[i][0]) ** 2 + (r[i + 1][1] - r[i][1]) ** 2) ** 0.5
    ans += a
print((ans / factorial(n)))

from itertools import combinations

n = int(eval(input()))
xy = [list(map(int, input().split())) for i in range(n)]
pair = list(combinations(xy, 2))
ans = 0
for p in pair:
    ans += ((p[0][0] - p[1][0]) ** 2 + (p[0][1] - p[1][1]) ** 2) ** 0.5
print((ans * (n - 1) / len(pair)))

-from itertools import permutations -from math import factorial +from itertools import combinations -root = list(permutations(xy, n)) +pair = list(combinations(xy, 2)) -for r in root: -    a = 0 -    for i in range(n - 1): -        a += ((r[i + 1][0] - r[i][0]) ** 2 + (r[i + 1][1] - r[i][1]) ** 2) ** 0.5 -    ans += a -print((ans / factorial(n))) +for p in pair: +    ans += ((p[0][0] - p[1][0]) ** 2 + (p[0][1] - p[1][1]) ** 2) ** 0.5 +print((ans * (n - 1) / len(pair)))