#include<iostream>
#include<fstream>
#define NMAX 2000000
#include<stdio.h>
#include<math.h>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,v[NMAX];

int main()
{int i,j,k=0;
	f>>n;
	for(i=2;i<=n;i++)
		v[i]=1;

	for(i=2;i<=n;i++)
  if(v[i]){k++;
     for(j=2*i;j<=n;j=j+i)
         v[j]=0; }
               
	
	g<<k;


return 0;
}