from sys import stdin

import statistics

from math import factorial

import math

from itertools import permutations



n = int(stdin.readline().rstrip())

li = [list(map(int,stdin.readline().rstrip().split())) for _ in range(n)]



lis = []

lin = list(permutations(li,n))



for i in range(len(lin)):

    liv = []

    for j in range(1,len(lin[0])):

        a = (lin[i][j-1][1]-lin[i][j][1])**2

        b = (lin[i][j-1][0]-lin[i][j][0])**2

        c = math.sqrt(a+b)

        liv.append(c)

    lis.append(sum(liv))

print((sum(lis)/len(lin)))
from itertools import permutations

import math



n = int(eval(input()))

li = [tuple(map(int,input().split())) for _ in range(n)]



# 2点間の距離

def length(x1,y1,x2,y2):

    return(math.sqrt(abs(x2-x1)**2+abs(y2-y1)**2))



point = 0



for i in permutations(li):

    for j in range(1,n):

        point += length(i[j-1][0],i[j-1][1],i[j][0],i[j][1])



print((point/math.factorial(n)))
from sys import stdin
import statistics
from math import factorial
import math
from itertools import permutations

n = int(stdin.readline().rstrip())
li = [list(map(int, stdin.readline().rstrip().split())) for _ in range(n)]
lis = []
lin = list(permutations(li, n))
for i in range(len(lin)):
    liv = []
    for j in range(1, len(lin[0])):
        a = (lin[i][j - 1][1] - lin[i][j][1]) ** 2
        b = (lin[i][j - 1][0] - lin[i][j][0]) ** 2
        c = math.sqrt(a + b)
        liv.append(c)
    lis.append(sum(liv))
print((sum(lis) / len(lin)))

from itertools import permutations
import math

n = int(eval(input()))
li = [tuple(map(int, input().split())) for _ in range(n)]
# 2点間の距離
def length(x1, y1, x2, y2):
    return math.sqrt(abs(x2 - x1) ** 2 + abs(y2 - y1) ** 2)


point = 0
for i in permutations(li):
    for j in range(1, n):
        point += length(i[j - 1][0], i[j - 1][1], i[j][0], i[j][1])
print((point / math.factorial(n)))

-from sys import stdin -import statistics -from math import factorial +from itertools import permutations -from itertools import permutations -n = int(stdin.readline().rstrip()) -li = [list(map(int, stdin.readline().rstrip().split())) for _ in range(n)] -lis = [] -lin = list(permutations(li, n)) -for i in range(len(lin)): -    liv = [] -    for j in range(1, len(lin[0])): -        a = (lin[i][j - 1][1] - lin[i][j][1]) ** 2 -        b = (lin[i][j - 1][0] - lin[i][j][0]) ** 2 -        c = math.sqrt(a + b) -        liv.append(c) -    lis.append(sum(liv)) -print((sum(lis) / len(lin))) +n = int(eval(input())) +li = [tuple(map(int, input().split())) for _ in range(n)] +# 2点間の距離 +def length(x1, y1, x2, y2): +    return math.sqrt(abs(x2 - x1) ** 2 + abs(y2 - y1) ** 2) + + +point = 0 +for i in permutations(li): +    for j in range(1, n): +        point += length(i[j - 1][0], i[j - 1][1], i[j][0], i[j][1]) +print((point / math.factorial(n)))