#include <iostream>
#include<fstream>

using namespace std;

int main()
{
    long n,i,j,nr; bool v[2000000];
    ifstream ci("ciur.in");
    ofstream sc("ciur.out");
    ci>>n;
    ci.close();
        nr=0;
     for (i=2;i<=n;i++)
       v[i]=1;
     v[1]=0;
      for (i=2;i<=n;i++)
       { if (v[i]!=0)
       {
        nr++;
           for ( j=i;j<=n;j=i+j)
            v[j]=0;
       }

       }
sc << nr;
   sc.close();
    return 0;
}