# ABC145 A

import itertools

si = lambda: eval(input())

ni = lambda: int(eval(input()))

nm = lambda: list(map(int, input().split()))

nl = lambda: list(map(int, input().split()))

n = ni()

L = [[] for i in range(n)]

D = []

for i in range(n):

    x,y = nm()

    L[i].append(x)

    L[i].append(y)



L = list(itertools.permutations(L))



for l in L:

    d = 0.0

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

        d += float(((l[i][0]-l[i+1][0])**2 + (l[i][1]-l[i+1][1])**2)**0.5)

    D.append(d)



ans = float(sum(D)/len(D))

print(ans)
from itertools import permutations

n=int(eval(input()))

l=[]

for i in range(n):

    x,y=list(map(int,input().split()))

    l.append((x,y))

dist=[]

for ll in list(permutations(l)):

    d=0.0

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

        d+=((ll[i][0]-ll[i+1][0])**2+(ll[i][1]-ll[i+1][1])**2)**0.5

    dist.append(d)

print((sum(dist)/len(dist)))

        
# ABC145 A
import itertools

si = lambda: eval(input())
ni = lambda: int(eval(input()))
nm = lambda: list(map(int, input().split()))
nl = lambda: list(map(int, input().split()))
n = ni()
L = [[] for i in range(n)]
D = []
for i in range(n):
    x, y = nm()
    L[i].append(x)
    L[i].append(y)
L = list(itertools.permutations(L))
for l in L:
    d = 0.0
    for i in range(len(l) - 1):
        d += float(((l[i][0] - l[i + 1][0]) ** 2 + (l[i][1] - l[i + 1][1]) ** 2) ** 0.5)
    D.append(d)
ans = float(sum(D) / len(D))
print(ans)

from itertools import permutations

n = int(eval(input()))
l = []
for i in range(n):
    x, y = list(map(int, input().split()))
    l.append((x, y))
dist = []
for ll in list(permutations(l)):
    d = 0.0
    for i in range(len(ll) - 1):
        d += ((ll[i][0] - ll[i + 1][0]) ** 2 + (ll[i][1] - ll[i + 1][1]) ** 2) ** 0.5
    dist.append(d)
print((sum(dist) / len(dist)))

-# ABC145 A -import itertools +from itertools import permutations -si = lambda: eval(input()) -ni = lambda: int(eval(input())) -nm = lambda: list(map(int, input().split())) -nl = lambda: list(map(int, input().split())) -n = ni() -L = [[] for i in range(n)] -D = [] +n = int(eval(input())) +l = [] -    x, y = nm() -    L[i].append(x) -    L[i].append(y) -L = list(itertools.permutations(L)) -for l in L: +    x, y = list(map(int, input().split())) +    l.append((x, y)) +dist = [] +for ll in list(permutations(l)): -    for i in range(len(l) - 1): -        d += float(((l[i][0] - l[i + 1][0]) ** 2 + (l[i][1] - l[i + 1][1]) ** 2) ** 0.5) -    D.append(d) -ans = float(sum(D) / len(D)) -print(ans) +    for i in range(len(ll) - 1): +        d += ((ll[i][0] - ll[i + 1][0]) ** 2 + (ll[i][1] - ll[i + 1][1]) ** 2) ** 0.5 +    dist.append(d) +print((sum(dist) / len(dist)))