/*
 * ciur.cpp
 *
 *  Created on: Oct 15, 2011
 *      Author: ruxy
 */

#include<cstdio>
#include<cmath>
using namespace std;
FILE *f,*g;


long int n=2000000;
char v[2000005];


void ciur(long int n)
{ int i,k;
  v[2]=1;
  for(i=3;i<=n;i=i+2)
	if(v[i]==0)
	  { v[i]=1;
		for(k=i*i;k<=n;k=k+i)
			v[k]=2;
	  }
}


int main()
{ long int d,contor=1,i;
  f=fopen("ciur.in","r");
  g=fopen("ciur.out","w");
  fscanf(f,"%d",&d);
  ciur(d);
  for(i=3;i<=d;i++)
    { if(v[i]==1)
	  contor++;
	}
  fprintf(g,"%d",contor);
  fclose(f); fclose(g);
  return 0;
}