Bulb Switcher

Medium

There are n bulbs initially off. On round i you toggle every i-th bulb (round 1 toggles all). After n rounds, return how many bulbs are on. A bulb ends on iff it has an odd number of divisors, i.e. it is a perfect square.

Example 1

Input:  n = 3
Output: 1

Example 2

Input:  n = 0
Output: 0

Example 3

Input:  n = 99
Output: 9

Constraints

• 0 <= n <= 10^6