#include <iostream>
#include <fstream>
#include <bitset>


std::ifstream f("ciur.in");
std::ofstream g("ciur.out");
int n, a[2000005];
std::bitset<2000005> viz;


int ciur()
{
	viz[0] = true;
	viz[1] = true;

	int s = 0;
	for (int i = 2; i <= n; i++) {
		if (viz[i] == true) continue; s++;
		for (int j = i + i; j <= n; j += i) {
			viz[j] = true;
		}
	}
	return s;
}


int main()
{
	f >> n;
	g << ciur() << std::endl;
	return 0;
}