import itertools

import math



n = int(eval(input()))

xy = []

for _ in range(n):

    xxyy = list(map(int, input().split()))

    xy.append(xxyy)



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

p = list(itertools.permutations(l))

dist = 0

for pp in p:

    preppi = pp[0]

    for ppi in pp[1:]:

        dist += math.sqrt((xy[ppi][0] - xy[preppi][0])**2 + (xy[ppi][1] - xy[preppi][1])**2)

        preppi = ppi

print((dist/len(p)))

import math



n = int(eval(input()))

xy = []

for _ in range(n):

    xxyy = list(map(int, input().split()))

    xy.append(xxyy)



dist = 0

for i, xyi in enumerate(xy):

    for xyj in xy[i+1:]:

        dist += math.sqrt((xyi[0] - xyj[0])**2 + (xyi[1] - xyj[1])**2)

print((dist*2/n))

import itertools
import math

n = int(eval(input()))
xy = []
for _ in range(n):
    xxyy = list(map(int, input().split()))
    xy.append(xxyy)
l = [i for i in range(n)]
p = list(itertools.permutations(l))
dist = 0
for pp in p:
    preppi = pp[0]
    for ppi in pp[1:]:
        dist += math.sqrt(
            (xy[ppi][0] - xy[preppi][0]) ** 2 + (xy[ppi][1] - xy[preppi][1]) ** 2
        )
        preppi = ppi
print((dist / len(p)))

import math

n = int(eval(input()))
xy = []
for _ in range(n):
    xxyy = list(map(int, input().split()))
    xy.append(xxyy)
dist = 0
for i, xyi in enumerate(xy):
    for xyj in xy[i + 1 :]:
        dist += math.sqrt((xyi[0] - xyj[0]) ** 2 + (xyi[1] - xyj[1]) ** 2)
print((dist * 2 / n))

-import itertools -l = [i for i in range(n)] -p = list(itertools.permutations(l)) -for pp in p: -    preppi = pp[0] -    for ppi in pp[1:]: -        dist += math.sqrt( -            (xy[ppi][0] - xy[preppi][0]) ** 2 + (xy[ppi][1] - xy[preppi][1]) ** 2 -        ) -        preppi = ppi -print((dist / len(p))) +for i, xyi in enumerate(xy): +    for xyj in xy[i + 1 :]: +        dist += math.sqrt((xyi[0] - xyj[0]) ** 2 + (xyi[1] - xyj[1]) ** 2) +print((dist * 2 / n))