#include <iostream>
#include <fstream>
#include <vector>
#include <cmath>

using namespace std;

int main()
{
	ifstream f("ciur.in");
	ofstream g("ciur.out");
	int n,k;
	f>>n;

	vector <bool> values (n+1,true);
	int lim = sqrt(n);
	for (int i = 2; i <= lim; i++){
		k = i;
		for (int j = 2; j*k <= n; j++)
			values[j*k] = false;
	}
	int contor = 0;
	for (int i = 2; i <= n; i++)
		if (values[i])
			contor++;
	g<<contor;
	g.close();


	return 0;
}