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

using namespace std;

bitset<2000000> ciur;
int n;
int cate = 0;

void generateCiur(){
	int gap = 2;
	while (gap <= n) {
		if (ciur[gap] == true){
			gap++;
		}
		else {
			for (int i = gap; i <= n; i += gap){
				ciur[i] = true;
			}
			gap++;
			cate++;
		}
	}
}


int main(){
	ifstream fin("ciur.in");
	fin >> n;
	fin.close();

	generateCiur();

	ofstream fout("ciur.out");
	fout << cate;
	fout.close();

	return 0;
}