#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;
}