import itertools

n = int(eval(input()))

x, y = [], []

f = 1

for i in range(n):

    f *= i + 1

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

    x.append(xi)

    y.append(yi)

p = [i for i in range(n)]

d = 0

for perm in itertools.permutations(p):

    for i in range(n - 1):

        d += ((x[perm[i]] - x[perm[i + 1]]) ** 2 + (y[perm[i]] - y[perm[i + 1]]) ** 2) ** 0.5

print((d / f))

    



import itertools

n = int(eval(input()))

x, y = [], []

for i in range(n):

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

    x.append(xi)

    y.append(yi)

d = 0

for i in range(n):

    for j in range(n):

        d += ((x[i] - x[j]) ** 2 + (y[i] - y[j]) ** 2) ** 0.5

print((d / n))

    



import itertools

n = int(eval(input()))
x, y = [], []
f = 1
for i in range(n):
    f *= i + 1
    xi, yi = list(map(int, input().split()))
    x.append(xi)
    y.append(yi)
p = [i for i in range(n)]
d = 0
for perm in itertools.permutations(p):
    for i in range(n - 1):
        d += (
            (x[perm[i]] - x[perm[i + 1]]) ** 2 + (y[perm[i]] - y[perm[i + 1]]) ** 2
        ) ** 0.5
print((d / f))

import itertools

n = int(eval(input()))
x, y = [], []
for i in range(n):
    xi, yi = list(map(int, input().split()))
    x.append(xi)
    y.append(yi)
d = 0
for i in range(n):
    for j in range(n):
        d += ((x[i] - x[j]) ** 2 + (y[i] - y[j]) ** 2) ** 0.5
print((d / n))

-f = 1 -    f *= i + 1 -p = [i for i in range(n)] -for perm in itertools.permutations(p): -    for i in range(n - 1): -        d += ( -            (x[perm[i]] - x[perm[i + 1]]) ** 2 + (y[perm[i]] - y[perm[i + 1]]) ** 2 -        ) ** 0.5 -print((d / f)) +for i in range(n): +    for j in range(n): +        d += ((x[i] - x[j]) ** 2 + (y[i] - y[j]) ** 2) ** 0.5 +print((d / n))