#include <iostream>
#include <fstream>
#include <math.h>
using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main() {
	int n, nr = 0;
	bool v[2000000] = { true };
	fin >> n;

	for (int i = 1; i <= n; i++)
		v[i] = true;

	for(int i = 2; i <= (int)sqrt(n); i++)
		if (v[i] == true) 
			for (int j = i * i; j <= n; j = j + i) 
				v[j] = false;

	for (int i = 2; i <= n; i++)
		if (v[i] == true) nr++;
	fout << nr;
	
}