import itertools

import math



N=int(eval(input()))

x=[]

y=[]



for _ in range(N):

    x1,y1=list(map(int,input().split()))

    x.append(x1)

    y.append(y1)

    



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

conb=itertools.permutations(conut, N)

total=0

for n,c in enumerate(conb):

    for i in range(N-1):

        n1=c[i]

        n2=c[i+1]

        h=math.sqrt((x[n1]-x[n2])**2 + (y[n1]-y[n2])**2)

        total+=h



print((total/(n+1)))





import itertools

N=int(eval(input()))

XY=[]

for _ in range(N):

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

    XY.append(tmp)

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

permutation = itertools.permutations(l, 2)

total=0

for p in permutation:

    i=p[0]

    j=p[1]

    total+=((XY[i][0] - XY[j][0])**2 + (XY[i][1] - XY[j][1])**2)**0.5



print((total/N))
import itertools
import math

N = int(eval(input()))
x = []
y = []
for _ in range(N):
    x1, y1 = list(map(int, input().split()))
    x.append(x1)
    y.append(y1)
conut = [i for i in range(N)]
conb = itertools.permutations(conut, N)
total = 0
for n, c in enumerate(conb):
    for i in range(N - 1):
        n1 = c[i]
        n2 = c[i + 1]
        h = math.sqrt((x[n1] - x[n2]) ** 2 + (y[n1] - y[n2]) ** 2)
        total += h
print((total / (n + 1)))

import itertools

N = int(eval(input()))
XY = []
for _ in range(N):
    tmp = list(map(int, input().split()))
    XY.append(tmp)
l = [i for i in range(N)]
permutation = itertools.permutations(l, 2)
total = 0
for p in permutation:
    i = p[0]
    j = p[1]
    total += ((XY[i][0] - XY[j][0]) ** 2 + (XY[i][1] - XY[j][1]) ** 2) ** 0.5
print((total / N))

-import math -x = [] -y = [] +XY = [] -    x1, y1 = list(map(int, input().split())) -    x.append(x1) -    y.append(y1) -conut = [i for i in range(N)] -conb = itertools.permutations(conut, N) +    tmp = list(map(int, input().split())) +    XY.append(tmp) +l = [i for i in range(N)] +permutation = itertools.permutations(l, 2) -for n, c in enumerate(conb): -    for i in range(N - 1): -        n1 = c[i] -        n2 = c[i + 1] -        h = math.sqrt((x[n1] - x[n2]) ** 2 + (y[n1] - y[n2]) ** 2) -        total += h -print((total / (n + 1))) +for p in permutation: +    i = p[0] +    j = p[1] +    total += ((XY[i][0] - XY[j][0]) ** 2 + (XY[i][1] - XY[j][1]) ** 2) ** 0.5 +print((total / N))