#include <fstream>
using namespace std;
unsigned char a[2000009];
int main()
{
	unsigned int m,y,i;
	double n;
	ifstream f1("ciur.in");
	f1>>n;
	m=1;
	for (y=3;y<=n;y=y+2)
		if (!a[y])
		{
			for (i=y+y;i<=n;i+=y) a[i]=1;
			m++;
		}
	ofstream f2("ciur.out");
	f2<<m;
	return 0;
}