from itertools import permutations

 

n = int(eval(input()))

n_ = 1

for i in range(n):

    n_ *= i+1

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

tot = 0

 

def dis(c,x,y):

  x1,y1 = c[x]

  x2,y2 = c[y]

  return ((x1-x2)**2 + (y1-y2)**2)**.5

 

for l in permutations(list(range(n))):

    d = 0

    cur = l[0]

    for x in l:

        d += dis(c,cur,x)

        cur = x

    tot += d/n_

print(tot)
#yandy

N = int(eval(input()))

 

paths = []

 

for _ in range(N):

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

    paths.append((x, y))

 

all_path_len = 0

 

for i in range(N):

    for j in range(N):

        if i == j:

            continue

        xa, ya = paths[i]

        xb, yb = paths[j]

        all_path_len += ((xa - xb) ** 2 + (ya - yb) ** 2) ** 0.5

 

ans = all_path_len / N

 

print(ans)
from itertools import permutations

n = int(eval(input()))
n_ = 1
for i in range(n):
    n_ *= i + 1
c = [tuple(map(int, input().split())) for _ in range(n)]
tot = 0


def dis(c, x, y):
    x1, y1 = c[x]
    x2, y2 = c[y]
    return ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5


for l in permutations(list(range(n))):
    d = 0
    cur = l[0]
    for x in l:
        d += dis(c, cur, x)
        cur = x
    tot += d / n_
print(tot)

# yandy
N = int(eval(input()))
paths = []
for _ in range(N):
    x, y = list(map(int, input().split()))
    paths.append((x, y))
all_path_len = 0
for i in range(N):
    for j in range(N):
        if i == j:
            continue
        xa, ya = paths[i]
        xb, yb = paths[j]
        all_path_len += ((xa - xb) ** 2 + (ya - yb) ** 2) ** 0.5
ans = all_path_len / N
print(ans)

-from itertools import permutations - -n = int(eval(input())) -n_ = 1 -for i in range(n): -    n_ *= i + 1 -c = [tuple(map(int, input().split())) for _ in range(n)] -tot = 0 - - -def dis(c, x, y): -    x1, y1 = c[x] -    x2, y2 = c[y] -    return ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5 - - -for l in permutations(list(range(n))): -    d = 0 -    cur = l[0] -    for x in l: -        d += dis(c, cur, x) -        cur = x -    tot += d / n_ -print(tot) +# yandy +N = int(eval(input())) +paths = [] +for _ in range(N): +    x, y = list(map(int, input().split())) +    paths.append((x, y)) +all_path_len = 0 +for i in range(N): +    for j in range(N): +        if i == j: +            continue +        xa, ya = paths[i] +        xb, yb = paths[j] +        all_path_len += ((xa - xb) ** 2 + (ya - yb) ** 2) ** 0.5 +ans = all_path_len / N +print(ans)