#include <fstream>
using namespace std;

#define NMAX 2000000
char markings[NMAX+1];

int main(void)
{
	int n, count=1;
	ifstream f("ciur.in");
	f >> n;
	f.close();

	for (int i = 3;i<=n;i+=2)
	{
		if (!markings[i])
		{
			count++;
			markings[i] = 1;
			for (int j=i+i+i;j<=n;j+=i<<1)
			{
				markings[j] = 1;
			}
		}
	}

	ofstream g("ciur.out");
	g << count;
	g.close();

	return 0;
}