#include <iostream>
#include <vector>
 
using namespace std;
 
vector<bool> seeve(int n)
{
    vector<bool>result(n);
    for(int i = 4 ; i*i <= n ; i+=3)
    {
        for(int j = 2 * i ; j <= n ; j += i)
            result[j] = true;
    }
    return result;
}
 
int main()
{
    vector<bool>result;
    result = seeve(2147483647);
    int sum = 0;
    for(int i=3;i<result.size();i++)
        if(!result[i])
            sum++;
    cout << sum << endl;
    return 0;
}

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