from itertools import permutations

from math import sqrt

import sys

sys.setrecursionlimit(10**9)

input = lambda: sys.stdin.readline().rstrip()

inpl = lambda: list(map(int,input().split()))

N = int(eval(input()))

xy = [inpl() for _ in range(N)]

S = sum(sum(sqrt(sum((xy[p[i+1]][k]-xy[p[i]][k])**2 for k in range(2)))

        for i in range(N-1)) for p in permutations(list(range(N))))

M = 1

for i in range(2,N+1): M*=i

print((S/M))
from math import sqrt

inpl = lambda: list(map(int,input().split()))

N = int(eval(input()))

xy = [inpl() for _ in range(N)]

def distance(i,j): return sqrt(sum((xy[i][k]-xy[j][k])**2 for k in range(2)))

S = sum(distance(i,j) for i in range(N-1) for j in range(i,N))

print((2*S/N))
from itertools import permutations
from math import sqrt
import sys

sys.setrecursionlimit(10**9)
input = lambda: sys.stdin.readline().rstrip()
inpl = lambda: list(map(int, input().split()))
N = int(eval(input()))
xy = [inpl() for _ in range(N)]
S = sum(
    sum(
        sqrt(sum((xy[p[i + 1]][k] - xy[p[i]][k]) ** 2 for k in range(2)))
        for i in range(N - 1)
    )
    for p in permutations(list(range(N)))
)
M = 1
for i in range(2, N + 1):
    M *= i
print((S / M))

from math import sqrt

inpl = lambda: list(map(int, input().split()))
N = int(eval(input()))
xy = [inpl() for _ in range(N)]


def distance(i, j):
    return sqrt(sum((xy[i][k] - xy[j][k]) ** 2 for k in range(2)))


S = sum(distance(i, j) for i in range(N - 1) for j in range(i, N))
print((2 * S / N))

-from itertools import permutations -import sys -sys.setrecursionlimit(10**9) -input = lambda: sys.stdin.readline().rstrip() -S = sum( -    sum( -        sqrt(sum((xy[p[i + 1]][k] - xy[p[i]][k]) ** 2 for k in range(2))) -        for i in range(N - 1) -    ) -    for p in permutations(list(range(N))) -) -M = 1 -for i in range(2, N + 1): -    M *= i -print((S / M)) + + +def distance(i, j): +    return sqrt(sum((xy[i][k] - xy[j][k]) ** 2 for k in range(2))) + + +S = sum(distance(i, j) for i in range(N - 1) for j in range(i, N)) +print((2 * S / N))