<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  # There are no primes less than 2

    # We are looking for primes in the range [2, n-1]
        upper_limit = n - 1

        prime = [True] * (upper_limit + 1)
        prime[0], prime[1] = False, False  # 0 and 1 are not prime numbers

        p = 2
        while p * p <= upper_limit:
            if prime[p]:
                for i in range(p * p, upper_limit + 1, p):
                    prime[i] = False
            p += 1
        prime_count = sum(prime)
        return prime_count

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