#include <fstream>
#include <bitset>

using namespace std;

bitset <2000001> b;
int n,nr;

int main ()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");

    f>>n;

    for (int i=2; i<=n; ++i)
        if (!b[i])
        {
            ++nr;
            for (int j=i+i; j<=n; j+=i)
                b[j]=1;
        }

    g<<nr;
    return 0;
}