#include <fstream>

using namespace std;

    int t[2000001];
int main()
{
    int n,i,j,nr;
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
        fin >> n;
   fin.close();
        t[1] = 1;
    for(i = 4;i<=n;i+=2)
        t[i] = 1;
            nr = 1;

        for(i = 3;i<=n;i+=2)
        {
            if (t[i] == 0)
            {
                nr++;

                for(j = i*i;j<=n;j+=i*i)
                    t[j] = 1;
            }
        }

   // for(i = 1;i<=n;i++)
     //       fout << t[i]<<" ";
     fout << nr<<"\n";

   fout.close();
    return 0;
}