N=int(eval(input()))

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



from math import sqrt

def dist(a,b):

    return sqrt((a[0]-b[0])**2 + (a[1]-b[1])**2)

from itertools import permutations

a=b=0

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

    b+=1

    for i in range(N-1):

        a+=dist(XY[p[i]], XY[p[i+1]])

print((a/b))
import sys

def main():

    input = sys.stdin.readline

    N=int(eval(input()))

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

    ans=0

    for i in range(N):

        for j in range(N):

            if i==j: continue

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

    print((ans/N))



if __name__ == '__main__':

    main()
N = int(eval(input()))
XY = [tuple(map(int, input().split())) for _ in range(N)]
from math import sqrt


def dist(a, b):
    return sqrt((a[0] - b[0]) ** 2 + (a[1] - b[1]) ** 2)


from itertools import permutations

a = b = 0
for p in permutations(list(range(N))):
    b += 1
    for i in range(N - 1):
        a += dist(XY[p[i]], XY[p[i + 1]])
print((a / b))

import sys


def main():
    input = sys.stdin.readline
    N = int(eval(input()))
    A = [tuple(map(int, input().split())) for _ in range(N)]
    ans = 0
    for i in range(N):
        for j in range(N):
            if i == j:
                continue
            ans += ((A[i][0] - A[j][0]) ** 2 + (A[i][1] - A[j][1]) ** 2) ** 0.5
    print((ans / N))


if __name__ == "__main__":
    main()

-N = int(eval(input())) -XY = [tuple(map(int, input().split())) for _ in range(N)] -from math import sqrt +import sys -def dist(a, b): -    return sqrt((a[0] - b[0]) ** 2 + (a[1] - b[1]) ** 2) +def main(): +    input = sys.stdin.readline +    N = int(eval(input())) +    A = [tuple(map(int, input().split())) for _ in range(N)] +    ans = 0 +    for i in range(N): +        for j in range(N): +            if i == j: +                continue +            ans += ((A[i][0] - A[j][0]) ** 2 + (A[i][1] - A[j][1]) ** 2) ** 0.5 +    print((ans / N)) -from itertools import permutations - -a = b = 0 -for p in permutations(list(range(N))): -    b += 1 -    for i in range(N - 1): -        a += dist(XY[p[i]], XY[p[i + 1]]) -print((a / b)) +if __name__ == "__main__": +    main()