class Solution {

public:

int countPrimes(int n) {

int counter_number = 0;

if(n == 0 | n==1)

counter_number = 0;

bool *Del = new bool[n];

Del[2] = false;

```
for(int i = 3;i <= n;i++)
{
if(i % 2 == 0)
Del[i] = true;
else
Del[i] = false;
}
for(int i = 3;i <= n;i += 2)
{
if(!Del[i])
{
if(i * i > n)
break;
for(int j = 3; i*j < n;j++)
{
Del[i*j] = true;
}
}
}
for(int i = 2;i < n;i++)
{
if(!Del[i])
counter_number += 1;
}
return counter_number;
}
```

};