```
public class Solution {
public int countPrimes(int n) {
if (n < 3) return 0;
boolean[] primes = new boolean[n];
int cnt = 0;
for (int i = 0; i < n; i++) primes[i] = true;
for (int k = 2; k < (float) n / k; k++)
{
if (primes[k])
{
for (int i = k; i < (float) n / k; i++) primes[i * k] = false;
}
}
for (int i = 2; i < n; i++) if (primes[i]) cnt++;
return cnt;
}
}
```