#include <fstream>

using namespace std;

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

bool a[2000001];




int main()
{
    int n,i,j,cont=0;
    in >> n;
    for(i=2;i<=n;i++)
    {
        a[i]=1;
    }


    for(i=2;i<=n;i++)
    {
        j=i;
        while(i*j<=n)
        {
            a[i*j]=0;
            j++;
        }
    }
    for(i=2;i<=n;i++)
    {
        if(a[i]==1)
        {
            cont++;
        }
    }





    out << cont;


    return 0;
}