<p>Given an integer <code>n</code>, return <em>the number of prime numbers that are strictly less than</em> <code>n</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

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

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 0
<strong>Output:</strong> 0
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> n = 1
<strong>Output:</strong> 0
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>0 &lt;= n &lt;= 5 * 10<sup>6</sup></code></li>
</ul>

class Solution:
    def countPrimes(self, n: int) -> int:

        if(n <= 2):
            return 0
        if(n == 3):
            return 1

        t = [True for _ in range(n)]
        t[0] = False
        t[1] = False
        t[2] = True
        t[3] = True
        i = 2
        to = int(math.sqrt(n))
        
        while i <= to :
            
            if(t[i] == True):
                j = i + i
                
                while j < n:
                    t[j] = False
                    j += i

            i += 1
        

        return sum(t)
    
        

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