Count Prime Numbers

Problem Statement

Determine how many prime numbers exist that are smaller than a given non-negative integer m.

Examples

Example 1:
Input: 15
Output: 6
Explanation: The prime numbers less than 15 are 2, 3, 5, 7, 11, and 13.

Example 2:
Input: 7
Output: 4
Explanation: The prime numbers less than 7 are 2, 3, 5, and 7 is not counted since we consider numbers strictly less than the input.

Constraints

• 0 ≤ m ≤ 5,000,000