#include <stdio.h>
using namespace std;
FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");
int n,nr;
char prim[250000];

int main()
{
  int j,m;
  fscanf(f,"%d",&n);
  for (m=2;m<=n;++m)
  {
    if((prim[m>>3] & (1<<(m&7)))==0)
    {
      ++nr;
      for (j=(m+m);j<=(n<<2);j+=m)
        prim[j>>3]|=(1<<(j&7));
    }
  }
  fprintf(g,"%d",nr); 
  return 0;
}