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

FILE *f,*g;

bitset <2100000>prim;
//int prim[1000];
  long n,i,j,c;
int main(){
  f=fopen("ciur.in","r");
  g=fopen("ciur.out","w");
  
  

  fscanf(f,"%ld",&n);
  
  //  for(i=4;i<=n;i+=2) prim[i]=1;
    for (i=3;i<=n;i+=2)  
           if (!prim[i]){  
               c++;  
               for (j=3*i;j<=n;j+=2*i)  
                   prim[j]=1;  
           }  

 
  fprintf(g,"%ld",c);
  
  
  
  fclose(f);
  fclose(g);
  return 0;
}