```
def countPrimes(self, n):
"""
:type n: int
:rtype: int
"""
if n<=2:
return 0
isPrime=[1]*n
isPrime[0]=0
isPrime[1]=0
for i in range(2,int(n**0.5)+1):
for j in range(2,int(n/i)+1):
if i*j<n:
isPrime[i*j]=0
return sum(isPrime)
```