import itertools

n = int(eval(input()))

xy = [list(map(int, input().split())) for _ in range(n)]



ans = []

X = 0

for v in itertools.permutations(list(range(n))):

  cnt = 0

  X += 1

  for i in range(n-1):

    x1,y1 = xy[v[0]][0], xy[v[0]][1]

    x2,y2 = xy[v[1]][0], xy[v[1]][1]

    cnt += ((x1-x2)**2 + (y1-y2)**2)**0.5

  ans.append(cnt)

print((sum(ans)/X))
import itertools

n = int(eval(input()))

xy = [list(map(int, input().split())) for _ in range(n)]



ans = []

for v in itertools.permutations(list(range(n)), n):

    a = 0

    for i in range(len(v)-1):

        x1,y1 = xy[v[i]][0], xy[v[i]][1]

        x2,y2 = xy[v[i+1]][0], xy[v[i+1]][1]

        a += ((x1-x2)**2+(y1-y2)**2)**0.5

    ans.append(a)

print((sum(ans)/len(ans)))
import itertools

n = int(eval(input()))
xy = [list(map(int, input().split())) for _ in range(n)]
ans = []
X = 0
for v in itertools.permutations(list(range(n))):
    cnt = 0
    X += 1
    for i in range(n - 1):
        x1, y1 = xy[v[0]][0], xy[v[0]][1]
        x2, y2 = xy[v[1]][0], xy[v[1]][1]
        cnt += ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5
    ans.append(cnt)
print((sum(ans) / X))

import itertools

n = int(eval(input()))
xy = [list(map(int, input().split())) for _ in range(n)]
ans = []
for v in itertools.permutations(list(range(n)), n):
    a = 0
    for i in range(len(v) - 1):
        x1, y1 = xy[v[i]][0], xy[v[i]][1]
        x2, y2 = xy[v[i + 1]][0], xy[v[i + 1]][1]
        a += ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5
    ans.append(a)
print((sum(ans) / len(ans)))

-X = 0 -for v in itertools.permutations(list(range(n))): -    cnt = 0 -    X += 1 -    for i in range(n - 1): -        x1, y1 = xy[v[0]][0], xy[v[0]][1] -        x2, y2 = xy[v[1]][0], xy[v[1]][1] -        cnt += ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5 -    ans.append(cnt) -print((sum(ans) / X)) +for v in itertools.permutations(list(range(n)), n): +    a = 0 +    for i in range(len(v) - 1): +        x1, y1 = xy[v[i]][0], xy[v[i]][1] +        x2, y2 = xy[v[i + 1]][0], xy[v[i + 1]][1] +        a += ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5 +    ans.append(a) +print((sum(ans) / len(ans)))