Buggy python submission (verdict: Runtime Error):
import sys, re
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians
from itertools import accumulate, permutations, combinations, product, groupby
from operator import itemgetter, mul
from copy import deepcopy, copy
from string import ascii_lowercase, ascii_uppercase, digits
from bisect import bisect, bisect_left
from fractions import gcd
from heapq import heappush, heappop
from functools import reduce
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
def ZIP(n): return zip(*(MAP() for _ in range(n)))
import numpy as np
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7

def dist(p1, p2):
	p1 = np.array(p1)
	p2 = np.array(p2)
	return np.linalg.norm(p1-p2)

N = INT()
xy = [LIST() for _ in range(N)]

distance = 0
cnt = 0

for p in permutations(xy, N):
	cnt += 1
	for i in range(N-1):
		distance += dist(p[i], p[i+1])

print(distance/cnt)

Fixed submission:
import sys, re
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians
from itertools import accumulate, permutations, combinations, product, groupby
from operator import itemgetter, mul
from copy import deepcopy, copy
from string import ascii_lowercase, ascii_uppercase, digits
from bisect import bisect, bisect_left
from fractions import gcd
from heapq import heappush, heappop
from functools import reduce
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
def ZIP(n): return zip(*(MAP() for _ in range(n)))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7

def dist(p1, p2):
	return sqrt((p1[0]-p2[0])**2 + (p1[1]-p2[1])**2)

N = INT()
xy = [LIST() for _ in range(N)]

distance = 0
cnt = 0

for p in permutations(xy, N):
	cnt += 1
	for i in range(N-1):
		distance += dist(p[i], p[i+1])

print(distance/cnt)

Buggy python submission (verdict: Time Limit Exceeded):
import sys, re
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians
from itertools import accumulate, permutations, combinations, product, groupby
from operator import itemgetter, mul
from copy import deepcopy, copy
from string import ascii_lowercase, ascii_uppercase, digits
from bisect import bisect, bisect_left
from fractions import gcd
from heapq import heappush, heappop
from functools import reduce
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
def ZIP(n): return zip(*(MAP() for _ in range(n)))
import numpy as np
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7

def dist(p1, p2):
	p1 = np.array(p1)
	p2 = np.array(p2)
	return np.linalg.norm(p1-p2)

N = INT()
xy = [LIST() for _ in range(N)]

distance = 0
cnt = 0

for p in permutations(xy, N):
	cnt += 1
	for i in range(N-1):
		distance += dist(p[i], p[i+1])

print(distance/cnt)

Fixed submission:
import sys, re
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, radians
from itertools import accumulate, permutations, combinations, product, groupby
from operator import itemgetter, mul
from copy import deepcopy, copy
from string import ascii_lowercase, ascii_uppercase, digits
from bisect import bisect, bisect_left
from fractions import gcd
from heapq import heappush, heappop
from functools import reduce
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
def ZIP(n): return zip(*(MAP() for _ in range(n)))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10 ** 9 + 7

def dist(p1, p2):
	return sqrt((p1[0]-p2[0])**2 + (p1[1]-p2[1])**2)

N = INT()
xy = [LIST() for _ in range(N)]

distance = 0
cnt = 0

for p in permutations(xy, N):
	cnt += 1
	for i in range(N-1):
		distance += dist(p[i], p[i+1])

print(distance/cnt)