#include <fstream>
#include <iostream>
#include <math.h>

using namespace std;

bool a[2000000];
int rez = 0;

void Sieve (int x)
{
	for (int i=2; i<=(int)(sqrt((double) x)); i++)
		if (a[i]==0)
		{
			rez++;
			for (int j = 2; j<=x/i; j++)
				a[j*i]=1;
		}
}

int main ()
{
    ifstream afile ("ciur.in");
    ofstream bfile ("ciur.out");
	int n;
	afile>>n;
	Sieve(n);
	bfile<<rez;
 return 0;   
}