from itertools import permutations

n= int(eval(input()))

ls = []

for i in range(n):

    a = list(map(int,input().split()))

    ls.append(a)

ans = []

for i in permutations(ls,n):

    #print(i)

    result = 0

    for j in range(n-1):

        result += (((i[j][0]-i[j+1][0])**2+(i[j][1]-i[j+1][1])**2)**(1/2))

    ans.append(result)



ans = (1/len(ans))*sum(ans)

print(ans)
#<100q.順列全探索>

#<15>

from itertools import combinations

n = int(eval(input()))

town = []

for i in range(n):

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

    town.append((x,y))



ans = 0

for i, j in combinations(town, 2):

    

    ans += ((i[0] - j[0]) ** 2 + (i[1] - j[1]) ** 2) ** (0.5)

print((2 * ans / n))

    

    

from itertools import permutations

n = int(eval(input()))
ls = []
for i in range(n):
    a = list(map(int, input().split()))
    ls.append(a)
ans = []
for i in permutations(ls, n):
    # print(i)
    result = 0
    for j in range(n - 1):
        result += ((i[j][0] - i[j + 1][0]) ** 2 + (i[j][1] - i[j + 1][1]) ** 2) ** (
            1 / 2
        )
    ans.append(result)
ans = (1 / len(ans)) * sum(ans)
print(ans)

# <100q.順列全探索>
# <15>
from itertools import combinations

n = int(eval(input()))
town = []
for i in range(n):
    x, y = list(map(int, input().split()))
    town.append((x, y))
ans = 0
for i, j in combinations(town, 2):
    ans += ((i[0] - j[0]) ** 2 + (i[1] - j[1]) ** 2) ** (0.5)
print((2 * ans / n))

-from itertools import permutations +# <100q.順列全探索> +# <15> +from itertools import combinations -ls = [] +town = [] -    a = list(map(int, input().split())) -    ls.append(a) -ans = [] -for i in permutations(ls, n): -    # print(i) -    result = 0 -    for j in range(n - 1): -        result += ((i[j][0] - i[j + 1][0]) ** 2 + (i[j][1] - i[j + 1][1]) ** 2) ** ( -            1 / 2 -        ) -    ans.append(result) -ans = (1 / len(ans)) * sum(ans) -print(ans) +    x, y = list(map(int, input().split())) +    town.append((x, y)) +ans = 0 +for i, j in combinations(town, 2): +    ans += ((i[0] - j[0]) ** 2 + (i[1] - j[1]) ** 2) ** (0.5) +print((2 * ans / n))