Description

Count the number of prime numbers up to a non-negative number, n.

A prime number is a numeral that is greater than 1 and cannot be divided evenly by any other number except 1 and itself. If a number can be divided evenly by any other number not counting itself and 1, it is not prime and is referred to as a composite number.

Example 1:

Input: 2
Output: 1

Example 2:

Input: 10
Output: 4