import itertools

import math

N=int(eval(input()))

T=[None]*N

for i in range(N):

    T[i] = list(map(int,input().split()))



seq=[i for i in range(N)]

kumi=list(itertools.permutations(seq))

L_sum=0

for i in range(len(kumi)):

    for j in range(N-1):

        L_sum+=math.sqrt((T[kumi[i][j]-1][0]-T[kumi[i][j+1]-1][0])**2+(T[kumi[i][j]-1][1]-T[kumi[i][j+1]-1][1])**2)

        #print(kumi[i][j],kumi[i][j+1])

        #,T[kumi[i][j+1]-1][0],T[kumi[i][j]-1][1],T[kumi[i][j+1]-1][1])

num=1

for i in range(1,N+1):

    num*=i

#print(L_sum)

print((L_sum/num))
# coding: utf-8

import math

import itertools

N = int(eval(input()))

R  =[]

for i in range(N):

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

    R.append([x, y])

#print(R[0][0])

#L = copy.deepcopy(R)

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

p = list(itertools.permutations(l,N))

S = 0

#print(p)

for v in p:

    for i in range(N-1):

        S += math.sqrt((R[v[i]][0]-R[v[i+1]][0])**2+(R[v[i]][1]-R[v[i+1]][1])**2)



ans = S / len(p)

print(ans)
import itertools
import math

N = int(eval(input()))
T = [None] * N
for i in range(N):
    T[i] = list(map(int, input().split()))
seq = [i for i in range(N)]
kumi = list(itertools.permutations(seq))
L_sum = 0
for i in range(len(kumi)):
    for j in range(N - 1):
        L_sum += math.sqrt(
            (T[kumi[i][j] - 1][0] - T[kumi[i][j + 1] - 1][0]) ** 2
            + (T[kumi[i][j] - 1][1] - T[kumi[i][j + 1] - 1][1]) ** 2
        )
        # print(kumi[i][j],kumi[i][j+1])
        # ,T[kumi[i][j+1]-1][0],T[kumi[i][j]-1][1],T[kumi[i][j+1]-1][1])
num = 1
for i in range(1, N + 1):
    num *= i
# print(L_sum)
print((L_sum / num))

# coding: utf-8
import math
import itertools

N = int(eval(input()))
R = []
for i in range(N):
    x, y = list(map(int, input().split()))
    R.append([x, y])
# print(R[0][0])
# L = copy.deepcopy(R)
l = [i for i in range(N)]
p = list(itertools.permutations(l, N))
S = 0
# print(p)
for v in p:
    for i in range(N - 1):
        S += math.sqrt(
            (R[v[i]][0] - R[v[i + 1]][0]) ** 2 + (R[v[i]][1] - R[v[i + 1]][1]) ** 2
        )
ans = S / len(p)
print(ans)

+# coding: utf-8 +import math -import math -T = [None] * N +R = [] -    T[i] = list(map(int, input().split())) -seq = [i for i in range(N)] -kumi = list(itertools.permutations(seq)) -L_sum = 0 -for i in range(len(kumi)): -    for j in range(N - 1): -        L_sum += math.sqrt( -            (T[kumi[i][j] - 1][0] - T[kumi[i][j + 1] - 1][0]) ** 2 -            + (T[kumi[i][j] - 1][1] - T[kumi[i][j + 1] - 1][1]) ** 2 +    x, y = list(map(int, input().split())) +    R.append([x, y]) +# print(R[0][0]) +# L = copy.deepcopy(R) +l = [i for i in range(N)] +p = list(itertools.permutations(l, N)) +S = 0 +# print(p) +for v in p: +    for i in range(N - 1): +        S += math.sqrt( +            (R[v[i]][0] - R[v[i + 1]][0]) ** 2 + (R[v[i]][1] - R[v[i + 1]][1]) ** 2 -        # print(kumi[i][j],kumi[i][j+1]) -        # ,T[kumi[i][j+1]-1][0],T[kumi[i][j]-1][1],T[kumi[i][j+1]-1][1]) -num = 1 -for i in range(1, N + 1): -    num *= i -# print(L_sum) -print((L_sum / num)) +ans = S / len(p) +print(ans)