#include <fstream>
using namespace std;

ifstream is("ciur.in");
ofstream os("ciur.out");

int N, cnt;
char p[2000001];

int main()
{
	is >> N;
	for(int i = 2; i <= N; ++i)
	{
		p[i] = 1;
	}
	for(int i = 2; i <= N; ++i)
	{
		if(p[i])
		{
			++cnt;
			for(int j = i + i; j <= N; j += i)
			{
				p[j] = 0;
			}
		}
	}
	os << cnt;
	is.close();
	os.close();
	return 0;
}