from itertools import permutations



n = int(eval(input()))

x = [0] * n

y = [0] * n



for i in range(n):

    x[i], y[i] = [int(j) for j in input().split()]



root = list(permutations(list(range(0,n))))

dist = 0



for r in root:

    for i in range(1,n):

        dist += ((x[r[i]]-x[r[i-1]])**2 + (y[r[i]]-y[r[i-1]])**2)**0.5



print((dist/len(root)))
import sys



readline = sys.stdin.readline

MOD = 10 ** 9 + 7

INF = float('INF')

sys.setrecursionlimit(10 ** 5)





def main():

    from itertools import permutations

    from math import factorial



    N = int(readline())

    mat = []

    s = 0



    for _ in range(N):

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

        mat.append([x, y])



    for per in permutations(list(range(N))):

        for i in range(N - 1):

            x1, y1 = mat[per[i]]

            x2, y2 = mat[per[i + 1]]

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



    print((s / factorial(N)))





if __name__ == '__main__':

    main()

from itertools import permutations

n = int(eval(input()))
x = [0] * n
y = [0] * n
for i in range(n):
    x[i], y[i] = [int(j) for j in input().split()]
root = list(permutations(list(range(0, n))))
dist = 0
for r in root:
    for i in range(1, n):
        dist += ((x[r[i]] - x[r[i - 1]]) ** 2 + (y[r[i]] - y[r[i - 1]]) ** 2) ** 0.5
print((dist / len(root)))

import sys

readline = sys.stdin.readline
MOD = 10**9 + 7
INF = float("INF")
sys.setrecursionlimit(10**5)


def main():
    from itertools import permutations
    from math import factorial

    N = int(readline())
    mat = []
    s = 0
    for _ in range(N):
        x, y = list(map(int, readline().split()))
        mat.append([x, y])
    for per in permutations(list(range(N))):
        for i in range(N - 1):
            x1, y1 = mat[per[i]]
            x2, y2 = mat[per[i + 1]]
            s += ((x2 - x1) ** 2 + (y2 - y1) ** 2) ** 0.5
    print((s / factorial(N)))


if __name__ == "__main__":
    main()

-from itertools import permutations +import sys -n = int(eval(input())) -x = [0] * n -y = [0] * n -for i in range(n): -    x[i], y[i] = [int(j) for j in input().split()] -root = list(permutations(list(range(0, n)))) -dist = 0 -for r in root: -    for i in range(1, n): -        dist += ((x[r[i]] - x[r[i - 1]]) ** 2 + (y[r[i]] - y[r[i - 1]]) ** 2) ** 0.5 -print((dist / len(root))) +readline = sys.stdin.readline +MOD = 10**9 + 7 +INF = float("INF") +sys.setrecursionlimit(10**5) + + +def main(): +    from itertools import permutations +    from math import factorial + +    N = int(readline()) +    mat = [] +    s = 0 +    for _ in range(N): +        x, y = list(map(int, readline().split())) +        mat.append([x, y]) +    for per in permutations(list(range(N))): +        for i in range(N - 1): +            x1, y1 = mat[per[i]] +            x2, y2 = mat[per[i + 1]] +            s += ((x2 - x1) ** 2 + (y2 - y1) ** 2) ** 0.5 +    print((s / factorial(N))) + + +if __name__ == "__main__": +    main()