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

using namespace std;

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

const int NMAX = 2000000;

bitset<NMAX + 1> check;

int eratostene(int x) {

	int nrPrimes = 0;

	for(int i = 2; i * i <= x; ++i) {
		if(check[i] == 0)
			for(int j = i * i; j <= x; j += i)
				check[j] = 1;
	}

	for(int i = 2; i <= x ; ++i)
		if(check[i] == 0)
			nrPrimes++;

	return nrPrimes;
}

int main() {

	int x;

	fin >> x;

	fout << eratostene(x);

	return 0;
}