import itertools as it

n = int(eval(input()))

zahyou = []

for i in range(n):

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

    zahyou.append((x,y))

perm = list(it.permutations(list(range(n)),n))

ans = 0

for zyu in perm:

    for i in range(n-1):

        ans += ((zahyou[zyu[i]][0] - zahyou[zyu[i+1]][0])**2 +(zahyou[zyu[i]][1] - zahyou[zyu[i+1]][1])**2 )**.5

ans /=len(perm)

print(ans)

import math

n = int(eval(input()))

dist = [[0]*n for _ in range(n)]

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

for i in range(n):

    for j in range(n):

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

from itertools import permutations

per = list(permutations([k for k in range(n)]))

count = 0

for pe in per:

    for l in range(n-1):

        count += dist[pe[l]][pe[l+1]]

ans = count/math.factorial(n)

print(ans)

import itertools as it

n = int(eval(input()))
zahyou = []
for i in range(n):
    x, y = list(map(int, input().split()))
    zahyou.append((x, y))
perm = list(it.permutations(list(range(n)), n))
ans = 0
for zyu in perm:
    for i in range(n - 1):
        ans += (
            (zahyou[zyu[i]][0] - zahyou[zyu[i + 1]][0]) ** 2
            + (zahyou[zyu[i]][1] - zahyou[zyu[i + 1]][1]) ** 2
        ) ** 0.5
ans /= len(perm)
print(ans)

import math

n = int(eval(input()))
dist = [[0] * n for _ in range(n)]
pos = [tuple(map(int, input().split())) for _ in range(n)]
for i in range(n):
    for j in range(n):
        dist[i][j] = (
            (pos[i][0] - pos[j][0]) ** 2 + (pos[i][1] - pos[j][1]) ** 2
        ) ** 0.5
from itertools import permutations

per = list(permutations([k for k in range(n)]))
count = 0
for pe in per:
    for l in range(n - 1):
        count += dist[pe[l]][pe[l + 1]]
ans = count / math.factorial(n)
print(ans)

-import itertools as it +import math -zahyou = [] +dist = [[0] * n for _ in range(n)] +pos = [tuple(map(int, input().split())) for _ in range(n)] -    x, y = list(map(int, input().split())) -    zahyou.append((x, y)) -perm = list(it.permutations(list(range(n)), n)) -ans = 0 -for zyu in perm: -    for i in range(n - 1): -        ans += ( -            (zahyou[zyu[i]][0] - zahyou[zyu[i + 1]][0]) ** 2 -            + (zahyou[zyu[i]][1] - zahyou[zyu[i + 1]][1]) ** 2 +    for j in range(n): +        dist[i][j] = ( +            (pos[i][0] - pos[j][0]) ** 2 + (pos[i][1] - pos[j][1]) ** 2 -ans /= len(perm) +from itertools import permutations + +per = list(permutations([k for k in range(n)])) +count = 0 +for pe in per: +    for l in range(n - 1): +        count += dist[pe[l]][pe[l + 1]] +ans = count / math.factorial(n)