from itertools import permutations

from math import sqrt



N = int(eval(input()))

xy = []

for _ in range(N):

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

    xy.append((x, y))





_sum = 0

for p in permutations(list(range(N))):

    s = p[0]

    x, y = xy[s]

    for i, pi in enumerate(p):

        if i == 0:

            continue

        nx, ny = xy[pi]

        d = (nx-x)**2 + (ny-y)**2

        _sum += sqrt(d)



a = 1

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

    a *= i

print((_sum/a))

from math import hypot



N = int(eval(input()))

XY = [tuple(map(int, input().split())) for _ in range(N)]



_sum = 0

for xi, yi in XY:

    for xj, yj in XY:

        _sum += hypot(xi-xj, yi-yj)



print((_sum/N))

from itertools import permutations
from math import sqrt

N = int(eval(input()))
xy = []
for _ in range(N):
    x, y = list(map(int, input().split()))
    xy.append((x, y))
_sum = 0
for p in permutations(list(range(N))):
    s = p[0]
    x, y = xy[s]
    for i, pi in enumerate(p):
        if i == 0:
            continue
        nx, ny = xy[pi]
        d = (nx - x) ** 2 + (ny - y) ** 2
        _sum += sqrt(d)
a = 1
for i in range(1, N + 1):
    a *= i
print((_sum / a))

from math import hypot

N = int(eval(input()))
XY = [tuple(map(int, input().split())) for _ in range(N)]
_sum = 0
for xi, yi in XY:
    for xj, yj in XY:
        _sum += hypot(xi - xj, yi - yj)
print((_sum / N))

-from itertools import permutations -from math import sqrt +from math import hypot -xy = [] -for _ in range(N): -    x, y = list(map(int, input().split())) -    xy.append((x, y)) +XY = [tuple(map(int, input().split())) for _ in range(N)] -for p in permutations(list(range(N))): -    s = p[0] -    x, y = xy[s] -    for i, pi in enumerate(p): -        if i == 0: -            continue -        nx, ny = xy[pi] -        d = (nx - x) ** 2 + (ny - y) ** 2 -        _sum += sqrt(d) -a = 1 -for i in range(1, N + 1): -    a *= i -print((_sum / a)) +for xi, yi in XY: +    for xj, yj in XY: +        _sum += hypot(xi - xj, yi - yj) +print((_sum / N))