#include <stdio.h>
#include <bitset>
#define nmax 2000000
using namespace std;

bitset <nmax> viz;

int main(){
  int n;
  FILE *fin=fopen("ciur.in","r");
  FILE *fout=fopen("ciur.out","w");
  fscanf(fin,"%d",&n);
  int i,j;
  int nr=0;
  for(i=2;i<=n;i++){
      if(!viz[i]){
         //printf("%d\n",i);
         nr++;
         for(j=i;j<=n;j+=i)viz[j]=1;
      }
  }
  fprintf(fout,"%d\n",nr);
     
return 0;
}