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# 204. Count Primes

## Description

Count the number of prime numbers less than a non-negative number, n.

Example 1:

Input: n = 10
Output: 4
Explanation: There are 4 prime numbers less than 10, they are 2, 3, 5, 7.


Example 2:

Input: n = 0
Output: 0


Example 3:

Input: n = 1
Output: 0


Constraints:

• 0 <= n <= 5 * 106