#include <fstream>
using namespace std;
char markings[1000001];
int main(void)
{
	int n, count=1;
	ifstream f("ciur.in");
	f >> n;
	f.close();
	for (int i = 1;(i<<1)+1<=n;i+=1) {
		if (!markings[i]) {
			count++;			
			for (int j=i+i+i+1;(j<<1)+1<=n;j+=(i<<1)+1) {
				markings[j] = 1;
			}
		}
	}
	ofstream g("ciur.out");
	g << count;
	g.close();
	return 0;
}