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

FILE *f,*g;

bitset <2000001>prim;
//int prim[1000];

int main(){
  f=fopen("ciur.in","r");
  g=fopen("ciur.out","w");
  
  
  long n,i,j,c;
  fscanf(f,"%ld",&n);
  
  //for(i=4;i<=n;i+=2) prim[i]=1;
  c=1;
  for(i=3;i<=n;i+=2)
    if(!prim[i]){
      c++;
      for(j=i*i;j<=n;j+=2*i)prim[j]=1;
    }
  fprintf(g,"%ld",c);
  
  
  
  fclose(f);
  fclose(g);
  return 0;
}