#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool v[2000001];
int n,nr=0;
void edit_vector(int x)
{
	for (int i = 2; i <= n / x; i++)
	{
		v[x * i] = 1;
	}
}

int main()
{
	in >> n;
	for (int i = 2; i <= n; i++) {
		if (v[i] == 0) {
			nr++;
			edit_vector(i);
		}
	}
	out << nr;
}