#include <cstdlib>
#include <stdio.h>
using namespace std;
FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");
int n,nr;
char prim[2000001];

int main()
{
  int j,m;
  fscanf(f,"%d",&n);
  for (int k=2;k<=n;k++)
    prim[k]=1;
  for (m=2;m<=n;++m)
  {
//    cout<<"("<<m<<prim[m]<<")\n";
    if(prim[m])
    {
      ++nr;
      for (j=m+m;j<=n;j+=m)
        prim[j]=0;
    }
  }
  fprintf(g,"%d",nr); 
  return EXIT_SUCCESS;
}