# 2138~

# アイディア 2140

# permutationを使って，N!通りの経路を実際に作ってそれらの経路を足して最終的にpermutation数で割れば良い

# 実装2200



N = int(eval(input()))



X=[]

Y=[]

for _ in range(N):

    xi,yi = list(map(int,input().split()))

    X.append(xi)

    Y.append(yi)

XY = [[x,y] for x,y in zip(X,Y)]

import itertools



All = itertools.permutations(XY)

distance = 0

import math

for j,xy in enumerate(All):

    for i,xiyi in enumerate(xy):

        if i == 0:

            start = xiyi

            continue

        now = xiyi

        distance += math.sqrt((start[0]-now[0])**2+(start[1]-now[1])**2)

        start = now

    num = j

print((distance/(num+1)))



import itertools

import math

N = int(eval(input()))

P = [0] * N 

for i in range(N):

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

distance = 0

for root in itertools.permutations(P,N):

    start = root[0]

    for r in root:

        distance += pow((r[0]-start[0])**2 + (r[1]-start[1])**2,1/2)

        start = r

print((distance/math.factorial(N)))

# 2138~
# アイディア 2140
# permutationを使って，N!通りの経路を実際に作ってそれらの経路を足して最終的にpermutation数で割れば良い
# 実装2200
N = int(eval(input()))
X = []
Y = []
for _ in range(N):
    xi, yi = list(map(int, input().split()))
    X.append(xi)
    Y.append(yi)
XY = [[x, y] for x, y in zip(X, Y)]
import itertools

All = itertools.permutations(XY)
distance = 0
import math

for j, xy in enumerate(All):
    for i, xiyi in enumerate(xy):
        if i == 0:
            start = xiyi
            continue
        now = xiyi
        distance += math.sqrt((start[0] - now[0]) ** 2 + (start[1] - now[1]) ** 2)
        start = now
    num = j
print((distance / (num + 1)))

import itertools
import math

N = int(eval(input()))
P = [0] * N
for i in range(N):
    P[i] = list(map(int, input().split()))
distance = 0
for root in itertools.permutations(P, N):
    start = root[0]
    for r in root:
        distance += pow((r[0] - start[0]) ** 2 + (r[1] - start[1]) ** 2, 1 / 2)
        start = r
print((distance / math.factorial(N)))

-# 2138~ -# アイディア 2140 -# permutationを使って，N!通りの経路を実際に作ってそれらの経路を足して最終的にpermutation数で割れば良い -# 実装2200 -N = int(eval(input())) -X = [] -Y = [] -for _ in range(N): -    xi, yi = list(map(int, input().split())) -    X.append(xi) -    Y.append(yi) -XY = [[x, y] for x, y in zip(X, Y)] - -All = itertools.permutations(XY) -distance = 0 -for j, xy in enumerate(All): -    for i, xiyi in enumerate(xy): -        if i == 0: -            start = xiyi -            continue -        now = xiyi -        distance += math.sqrt((start[0] - now[0]) ** 2 + (start[1] - now[1]) ** 2) -        start = now -    num = j -print((distance / (num + 1))) +N = int(eval(input())) +P = [0] * N +for i in range(N): +    P[i] = list(map(int, input().split())) +distance = 0 +for root in itertools.permutations(P, N): +    start = root[0] +    for r in root: +        distance += pow((r[0] - start[0]) ** 2 + (r[1] - start[1]) ** 2, 1 / 2) +        start = r +print((distance / math.factorial(N)))