N = int(input())
pos = []
for n in range(N):
    x, y = map(int, input().split())
    pos.append((x, y))
import math
from itertools import permutations
list = [i for i in range(N)]
per = permutations(list, N)
ans = 0
for i in per:
    for j in range(N - 1):
        x1, y1 = pos[i[j]]
        x2, y2 = pos[i[j + 1]]
        ans += math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2)
for n in range(1, N + 1):
    ans /= n
print(ans)

122bd7974f402661d1ab0042f1fb7b64ff6d12e5
<mask token>

<mask token>
for n in range(N):
    x, y = map(int, input().split())
    pos.append((x, y))
<mask token>
for i in per:
    for j in range(N - 1):
        x1, y1 = pos[i[j]]
        x2, y2 = pos[i[j + 1]]
        ans += math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2)
for n in range(1, N + 1):
    ans /= n
print(ans)

N = int(input())
pos = []
for n in range(N):
    x, y = map(int, input().split())
    pos.append((x, y))
<mask token>
list = [i for i in range(N)]
per = permutations(list, N)
ans = 0
for i in per:
    for j in range(N - 1):
        x1, y1 = pos[i[j]]
        x2, y2 = pos[i[j + 1]]
        ans += math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2)
for n in range(1, N + 1):
    ans /= n
print(ans)

N = int(input())
pos = []
for n in range(N):
    x, y = map(int, input().split())
    pos.append((x, y))
import math
from itertools import permutations
list = [i for i in range(N)]
per = permutations(list, N)
ans = 0
for i in per:
    for j in range(N - 1):
        x1, y1 = pos[i[j]]
        x2, y2 = pos[i[j + 1]]
        ans += math.sqrt((x1 - x2) ** 2 + (y1 - y2) ** 2)
for n in range(1, N + 1):
    ans /= n
print(ans)
