#!/usr/bin/env python3

n = int(input())
ps = [list(map(int, input().split())) for _ in range(n)]
a = 10**18
for p in ps:
    s = 0
    for q in ps:
        s += ((p[0] - q[0]) ** 2 + (p[1] - q[1]) ** 2) ** 0.5
    a = min(a, s)
print(a / (n - 1))