Leetcode 204 Count Primes

class Solution:
    # @param {integer} n
    # @return {integer}
    def countPrimes(self, n):
        isPrime = [True] * max(n, 2)
        isPrime[0]=False; isPrime[1]=False
        x = 2
        while x*x < n:
            if isPrime[x]:
                p = x*x
                while p < n:
                    isPrime[p] = False
                    p += x
            x += 1
        return sum(isPrime)