import itertools



N = int(eval(input()))

x, y = [], []

for _ in range(N):

    _x, _y = list(map(int, input().split()))

    x.append(_x)

    y.append(_y)



ans = 0

paths = list(itertools.permutations(list(range(N))))

for p in paths:

    for i in range(N-1):

        s = p[i]

        d = p[i+1]

        ans += ((x[s] - x[d]) ** 2 + (y[s] - y[d]) ** 2) ** 0.5

ans /= len(paths)

print(ans)
from itertools import permutations



N = int(eval(input()))

x, y = [], []

for _ in range(N):

    _x, _y = list(map(int, input().split()))

    x.append(_x)

    y.append(_y)



al = list(permutations(list(range(N))))

ttmp = []

for a in al:

    tmp = 0

    h = a[0]

    for i in a[1:]:

        tmp += ((x[h] - x[i]) ** 2 + (y[h] - y[i]) ** 2) ** 0.5

        h = i

    ttmp.append(tmp)

print((sum(ttmp) / len(al)))
import itertools

N = int(eval(input()))
x, y = [], []
for _ in range(N):
    _x, _y = list(map(int, input().split()))
    x.append(_x)
    y.append(_y)
ans = 0
paths = list(itertools.permutations(list(range(N))))
for p in paths:
    for i in range(N - 1):
        s = p[i]
        d = p[i + 1]
        ans += ((x[s] - x[d]) ** 2 + (y[s] - y[d]) ** 2) ** 0.5
ans /= len(paths)
print(ans)

from itertools import permutations

N = int(eval(input()))
x, y = [], []
for _ in range(N):
    _x, _y = list(map(int, input().split()))
    x.append(_x)
    y.append(_y)
al = list(permutations(list(range(N))))
ttmp = []
for a in al:
    tmp = 0
    h = a[0]
    for i in a[1:]:
        tmp += ((x[h] - x[i]) ** 2 + (y[h] - y[i]) ** 2) ** 0.5
        h = i
    ttmp.append(tmp)
print((sum(ttmp) / len(al)))

-import itertools +from itertools import permutations -ans = 0 -paths = list(itertools.permutations(list(range(N)))) -for p in paths: -    for i in range(N - 1): -        s = p[i] -        d = p[i + 1] -        ans += ((x[s] - x[d]) ** 2 + (y[s] - y[d]) ** 2) ** 0.5 -ans /= len(paths) -print(ans) +al = list(permutations(list(range(N)))) +ttmp = [] +for a in al: +    tmp = 0 +    h = a[0] +    for i in a[1:]: +        tmp += ((x[h] - x[i]) ** 2 + (y[h] - y[i]) ** 2) ** 0.5 +        h = i +    ttmp.append(tmp) +print((sum(ttmp) / len(al)))