#include <fstream>
using namespace std;

ifstream is("ciur.in");
ofstream os("ciur.out");

int n;
bool ok[2000002];
int cnt;

int main()
{
    is >> n;
    for (int i = 2; i*i <= n; ++i)
        if ( !ok[i] )
            for (int j = 2; j*i <= n; ++j)
                ok[i*j] = true;

    for (int i = 2; i <= n; ++i)
        if ( !ok[i] )
            cnt++;

    os << cnt;

    is.close();
    os.close();
    return 0;
}