#include <fstream>

using namespace std;

const int VM = 2000001;
bool c[VM];

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

int main()
{
    int n;
    in >> n;
    for (int i=2; i*i<=n; i++)
    {
        if (!c[i])
        {
            for(int j=i*i; j<=n; j+=i)
            {
                c[j]=true;
            }
        }
    }
    in.close();
    int nr = 0;
    for (int i=2; i<=n; i++)
    {
        if (!c[i])
        {
            nr++;
        }
    }
    out << nr;
    out.close();
    return 0;
}