#include<fstream>

using namespace std;
bool ciur[2000000];
ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
int d,N,i,nr=0;


in>>N;


for ( d = 2; d< N; d++ )
  {if ( ciur[d] == 0 )
    {for ( i = d * d; i < N; i = i + d )
     {

      ciur[i] = 1;}
        nr++;}

  }
      out<<nr;

      return 0;
      }