#include <fstream>

using namespace std;

    int t[2000000];
int main()
{
    int n,i,j,nr;
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
        fin >> n;
   fin.close();

            nr = 1;
        for(i = 3;i<=n;i+=2)
        {
            if (t[i] == 0)
                for(j = i*i;j<=n;j+=2*i)
                    t[j] = 1;

        }

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

   fout.close();
    return 0;
}