#include <cstdio>

using namespace std;

#define maxN 2000005

int N;
bool p[maxN];

int main ()
{
	freopen ("ciur.in" , "r" , stdin);
	freopen ("ciur.out" , "w" , stdout);
	
	scanf ("%d" , &N);
	
	for (int i = 2 ; i <= N ; ++i)
		if (!p[i])
			for (int j = i + i ; j <= N ; j += i)
				p[j] = true;
	
	
	int cont = 0;
	
	for (int i = 2 ; i <= N ; ++i)
		if (!p[i])
			++cont;
	
	
	printf ("%d" , cont);
	
	return 0;
}