#include <fstream>


using namespace std;

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

bool v[2000001];
int main()
{   int n,i,gg=0,j;

    in>>n;

    for (i=2;i<=n;i++)
    {
        if (v[i]==0)
        {
            gg++;

            for(j=i*2;j<=n;j+=i)
            {
                v[j]=1;
            }
        }
    }
      out<<gg;

    return 0;
}