#include <fstream>
using namespace std;
int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    unsigned long long n,nr=0;
    bool ok;
    f>>n;
    for(unsigned long long i=2;i<=n;++i)
    {
        ok=true;
        for(unsigned long long j=2;j*j<=i&&ok;++j)
            if(i%j==0)
                ok=false;
        if(ok)
            ++nr;
    }
    g<<nr;
}