import sys
from math import sqrt
input = sys.stdin.readline
def dis(a, b):
return sqrt((a[0] - b[0]) ** 2 + ((a[1] - b[1]) ** 2))
n = int(input())
l = [[*map(int, input().split())] for i in range(n)]
ans = 1000000000
for i in range(0, n):
crt = 0
for j in range(0, n):
if i == j:
continue
crt += dis(l[i], l[j])
ans = min(ans, crt / (n - 1))
print(ans)