#include <fstream>

using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int n, v[2000005];

int main()
{
	int i, k;
	f >> n;
	for (i = 2;i <= 2000005;i++)
		v[i] = i;
	for (i = 2;i <= 2000005;i++)
		if (v[i])
		{
			k = 2;
			while (i*k <= 2000005)
			{
				v[i*k] = 0;
				k++;
			}
		}
	k = 0;
	for (i = 1;i <= n;i++)
		if (v[i])
			k++;
	g << k << "\n";
	return 0;
}