#include <math.h>
#include <fstream>
using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
int n, r;
bool v[2000005];
int main()
{	cin >> n;
	for (int i = 2; i <= n; i++) {
		if (v[i] == 0) {
			for (int d = i + i; d <= n; d += i)
				v[d] = 1;
			r++;}
	}
	cout << r;
	return 0;
}