from itertools import permutations

N = int(eval(input()))

comb = list(permutations([i for i in range(0, N)], N))

xy = []

for _ in range(N):

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

    xy.append([x, y])

ans = 0

for c in comb:

    for i in range(0, N-1):

        x = ((xy[c[i]][0] - xy[c[i+1]][0]) ** 2)

        y = ((xy[c[i]][1] - xy[c[i+1]][1]) ** 2)

        ans += (x + y) ** 0.5

print((ans/len(comb)))
from itertools import permutations

N = int(eval(input()))

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

ans = 0

li = list(permutations(list(range(N))))

l = len(list(permutations(list(range(N)))))

for i in li:

    for j in range(N-1):

        x1, x2 = xy[i[j]][0], xy[i[j+1]][0]

        y1, y2 = xy[i[j]][1], xy[i[j+1]][1]

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

print((ans/l))
from itertools import permutations

N = int(eval(input()))
comb = list(permutations([i for i in range(0, N)], N))
xy = []
for _ in range(N):
    x, y = list(map(int, input().split()))
    xy.append([x, y])
ans = 0
for c in comb:
    for i in range(0, N - 1):
        x = (xy[c[i]][0] - xy[c[i + 1]][0]) ** 2
        y = (xy[c[i]][1] - xy[c[i + 1]][1]) ** 2
        ans += (x + y) ** 0.5
print((ans / len(comb)))

from itertools import permutations

N = int(eval(input()))
xy = [list(map(int, input().split())) for _ in range(N)]
ans = 0
li = list(permutations(list(range(N))))
l = len(list(permutations(list(range(N)))))
for i in li:
    for j in range(N - 1):
        x1, x2 = xy[i[j]][0], xy[i[j + 1]][0]
        y1, y2 = xy[i[j]][1], xy[i[j + 1]][1]
        ans += ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5
print((ans / l))

-comb = list(permutations([i for i in range(0, N)], N)) -xy = [] -for _ in range(N): -    x, y = list(map(int, input().split())) -    xy.append([x, y]) +xy = [list(map(int, input().split())) for _ in range(N)] -for c in comb: -    for i in range(0, N - 1): -        x = (xy[c[i]][0] - xy[c[i + 1]][0]) ** 2 -        y = (xy[c[i]][1] - xy[c[i + 1]][1]) ** 2 -        ans += (x + y) ** 0.5 -print((ans / len(comb))) +li = list(permutations(list(range(N)))) +l = len(list(permutations(list(range(N))))) +for i in li: +    for j in range(N - 1): +        x1, x2 = xy[i[j]][0], xy[i[j + 1]][0] +        y1, y2 = xy[i[j]][1], xy[i[j + 1]][1] +        ans += ((x1 - x2) ** 2 + (y1 - y2) ** 2) ** 0.5 +print((ans / l))