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 sys

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]



t = 0

for i in range(N):

    for j in range(i, N):

        t += ((X[i] - X[j])**2 + (Y[i] - Y[j])**2)**0.5

print((2*t/N))
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 sys

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]
t = 0
for i in range(N):
    for j in range(i, N):
        t += ((X[i] - X[j]) ** 2 + (Y[i] - Y[j]) ** 2) ** 0.5
print((2 * t / N))

-from itertools import permutations as perm -import numpy as np -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)) +t = 0 +for i in range(N): +    for j in range(i, N): +        t += ((X[i] - X[j]) ** 2 + (Y[i] - Y[j]) ** 2) ** 0.5 +print((2 * t / N))