Almost prime

#include <bits/stdc++.h>
using namespace std;

vector <int> primes;
bool isprime[3000];

void sieve(int n)
{
    memset(isprime, true, sizeof(isprime));
    int limit = sqrt(n+1);
    isprime[0] = isprime[1] = false;
    for(int i = 4; i < n; i+=2) isprime[i] = false;
    primes.push_back(2);
    for(int i = 3; i <= n; i+=2){
        if(isprime[i]){
            primes.push_back(i);
            if(i <= limit){
                for(int j = i*i; j <= n; j += i*2){
                    isprime[j] = false;
                }
            }
        }
    }
}

int main()
{
    int n, c, p = 0;
    cin >> n;
    if(n < 6) cout << 0 << endl;
    else if(n >= 6 && n <= 10) cout << 2 << endl;
    else{
        sieve(n);
        for(int i = 11; i <= n; i++)
        {
            c = 0;
            for(int j = 0; j < primes.size(); j++){
                if(i%primes[j] == 0 && primes[j] <= i/2) c++;
                if(c == 2) {
                    p++;
                    break;
                }
            }
        }
        cout << p+2 << endl;
    }
    return 0;
}