#include<fstream>
int p[2000001];
using namespace std;
int main()
{  ifstream f("ciur.in");
    ofstream g("ciur.out");
    long n, i,j,nr=0;
      f>>n;
      for (i=2;i<=n;++i)
       if(p[i]==0)
       {
           nr++;
           for (j=i+i; j<=n;j+=i)
            p[j]=1;
       }
    g<<nr;
    f.close();
    g.close();
    return 0;
}