#include <fstream>

using namespace std;
int n;
bool viz[2000005];
void citire()
{
    ifstream fin ("ciur.in");
    fin>>n;
    fin.close();
}
void rezolvare()
{
    int i,p,nrprime=0;
    ofstream fout ("ciur.out");
    for (i=2;i*i<=n;i++)
    {
        if (viz[i]==0)
        {
            viz[i]=1;
            p=i;
            nrprime++;
            while (p<=n)
            {
                p=p+i;
                viz[p]=1;
            }
        }
    }

    for (i;i<=n;i++)
        if (viz[i]==0)
            nrprime++;
    fout<<nrprime;
    fout<<'\n';
    fout.close();
}
int main()
{
    citire();
    rezolvare();
    return 0;
}