import itertools

import math



N = int(eval(input()))

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



ans = 0

for perm in itertools.permutations([i for i in range(N)]):

    for i in range(N - 1):

        ans += ((P[perm[i]][0] - P[perm[i+1]][0]) ** 2

                + (P[perm[i]][1] - P[perm[i+1]][1]) ** 2) ** 0.5



print((ans / math.factorial(N)))

N = int(eval(input()))

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

ans = 0

for i in range(N):

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

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



print((2 * ans / N))

import itertools
import math

N = int(eval(input()))
P = [tuple(map(int, input().split())) for _ in range(N)]
ans = 0
for perm in itertools.permutations([i for i in range(N)]):
    for i in range(N - 1):
        ans += (
            (P[perm[i]][0] - P[perm[i + 1]][0]) ** 2
            + (P[perm[i]][1] - P[perm[i + 1]][1]) ** 2
        ) ** 0.5
print((ans / math.factorial(N)))

N = int(eval(input()))
P = [tuple(map(int, input().split())) for _ in range(N)]
ans = 0
for i in range(N):
    for j in range(i + 1, N):
        ans += ((P[i][0] - P[j][0]) ** 2 + (P[i][1] - P[j][1]) ** 2) ** 0.5
print((2 * ans / N))

-import itertools -import math - -for perm in itertools.permutations([i for i in range(N)]): -    for i in range(N - 1): -        ans += ( -            (P[perm[i]][0] - P[perm[i + 1]][0]) ** 2 -            + (P[perm[i]][1] - P[perm[i + 1]][1]) ** 2 -        ) ** 0.5 -print((ans / math.factorial(N))) +for i in range(N): +    for j in range(i + 1, N): +        ans += ((P[i][0] - P[j][0]) ** 2 + (P[i][1] - P[j][1]) ** 2) ** 0.5 +print((2 * ans / N))