#include <fstream>
#include <bitset>
using namespace std;
ifstream f ("ciur.in");
ofstream g ("ciur.out");
const int nmax=2e6+3;
bitset <nmax> v;
int n,sol;
int main()
{
      f>>n;
      ++sol;
      for(int i=3;i<=n;i+=2)
      {
            if(v[i]) continue;
            ++sol;
            if(1ll*i*i>n) continue;
            for(int j=i*i;j<=n;j+=i) v[j]=true;
      }
      g<<sol;
      return 0;
}