#include <fstream>
using namespace std;
bool v[2000100];
int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int n;
    fin>>n;
    int s=0;
    for (int i=2;i<=n;++i)
    {
        if (v[i]==0)
        {
        for (int j=i;j<=n/i;++j)
        {
            v[j*i]=1;
        }
        s++;
        }
    }
    fout<<s;
}