#include<fstream>
using namespace std;
int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
  int v[100]={0},n,i,goguta=0,j;
  in>>n;
  for(i=2;i<=n;i++)
    if(v[i]==0)
  {
      for(j=i+i;j<=n;j=j+i)
        v[j]=1;
      goguta++;
  }
  out<<goguta;
  return 0;
}