from itertools import permutations as perm

import sys

import math

import numpy as np

read = sys.stdin.buffer.read

readline = sys.stdin.buffer.readline

readlines = sys.stdin.buffer.readlines

N = int(readline())

XY = np.array(read().split(), np.int64)

X = XY[0::2]

Y = XY[1::2]



res = 0

cnt = 0

for p in perm(list(range(N))):

    for i in range(N - 1):

        res += math.sqrt((X[p[i + 1]] - X[p[i]])**2 + (Y[p[i + 1]] - Y[p[i]])**2)

    cnt += 1    

print((res/cnt))
from itertools import permutations as perm

import sys

import numpy as np

read = sys.stdin.buffer.read

readline = sys.stdin.buffer.readline

readlines = sys.stdin.buffer.readlines

N = int(readline())

XY = list(map(int, read().split()))

X = XY[0::2]

Y = XY[1::2]



res = 0

cnt = 0

for p in perm(list(range(N))):

    for i in range(N - 1):

        res += ((X[p[i + 1]] - X[p[i]])**2 + (Y[p[i + 1]] - Y[p[i]])**2)**0.5

    cnt += 1    

print((res/cnt))
from itertools import permutations as perm
import sys
import math
import numpy as np

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
N = int(readline())
XY = np.array(read().split(), np.int64)
X = XY[0::2]
Y = XY[1::2]
res = 0
cnt = 0
for p in perm(list(range(N))):
    for i in range(N - 1):
        res += math.sqrt((X[p[i + 1]] - X[p[i]]) ** 2 + (Y[p[i + 1]] - Y[p[i]]) ** 2)
    cnt += 1
print((res / cnt))

from itertools import permutations as perm
import sys
import numpy as np

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
N = int(readline())
XY = list(map(int, read().split()))
X = XY[0::2]
Y = XY[1::2]
res = 0
cnt = 0
for p in perm(list(range(N))):
    for i in range(N - 1):
        res += ((X[p[i + 1]] - X[p[i]]) ** 2 + (Y[p[i + 1]] - Y[p[i]]) ** 2) ** 0.5
    cnt += 1
print((res / cnt))

-import math -XY = np.array(read().split(), np.int64) +XY = list(map(int, read().split())) -        res += math.sqrt((X[p[i + 1]] - X[p[i]]) ** 2 + (Y[p[i + 1]] - Y[p[i]]) ** 2) +        res += ((X[p[i + 1]] - X[p[i]]) ** 2 + (Y[p[i + 1]] - Y[p[i]]) ** 2) ** 0.5