import itertools, math



n = int(eval(input()))

xy = []

kai = 1

for i in range(n):

    xy.append(list(map(int, input().split())))

    kai *= (i + 1)

    

cost = 0

for lst in itertools.permutations(list(range(n)), n):

    x = xy[lst[0]][0]

    y = xy[lst[0]][1]

    for num in lst:

        dx = xy[num][0] - x

        dy = xy[num][1] - y

        cost += math.sqrt(dx ** 2 + dy ** 2)

        x = xy[num][0]

        y = xy[num][1]

print((cost / kai))
import itertools



n = int(eval(input()))

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



def fact(n):

    if n == 1:

        return 1

    else:

        return n * fact(n - 1)



ans = 0

div = fact(n)

for lst in itertools.permutations(list(range(n)), n):

    start = xy[lst[0]]

    for pos in lst:

        dx = start[0] - xy[pos][0]

        dy = start[1] - xy[pos][1]

        d = (dx ** 2 + dy ** 2) ** 0.5

        ans += d / div

print(ans)

    
import itertools, math

n = int(eval(input()))
xy = []
kai = 1
for i in range(n):
    xy.append(list(map(int, input().split())))
    kai *= i + 1
cost = 0
for lst in itertools.permutations(list(range(n)), n):
    x = xy[lst[0]][0]
    y = xy[lst[0]][1]
    for num in lst:
        dx = xy[num][0] - x
        dy = xy[num][1] - y
        cost += math.sqrt(dx**2 + dy**2)
        x = xy[num][0]
        y = xy[num][1]
print((cost / kai))

import itertools

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


def fact(n):
    if n == 1:
        return 1
    else:
        return n * fact(n - 1)


ans = 0
div = fact(n)
for lst in itertools.permutations(list(range(n)), n):
    start = xy[lst[0]]
    for pos in lst:
        dx = start[0] - xy[pos][0]
        dy = start[1] - xy[pos][1]
        d = (dx**2 + dy**2) ** 0.5
        ans += d / div
print(ans)

-import itertools, math +import itertools -xy = [] -kai = 1 -for i in range(n): -    xy.append(list(map(int, input().split()))) -    kai *= i + 1 -cost = 0 +xy = [list(map(int, input().split())) for _ in range(n)] + + +def fact(n): +    if n == 1: +        return 1 +    else: +        return n * fact(n - 1) + + +ans = 0 +div = fact(n) -    x = xy[lst[0]][0] -    y = xy[lst[0]][1] -    for num in lst: -        dx = xy[num][0] - x -        dy = xy[num][1] - y -        cost += math.sqrt(dx**2 + dy**2) -        x = xy[num][0] -        y = xy[num][1] -print((cost / kai)) +    start = xy[lst[0]] +    for pos in lst: +        dx = start[0] - xy[pos][0] +        dy = start[1] - xy[pos][1] +        d = (dx**2 + dy**2) ** 0.5 +        ans += d / div +print(ans)