#include <iostream>
#include <vector>
#include <math.h>
#include <algorithm>
#include <iomanip>
#include <array>
#include <fstream>

using namespace std;

void printVector(vector<int64_t> v) {
	for (auto& el : v) {
		cout << el << " ";
	}
	cout << "\n";
}

int maximAdi(vector<int64_t> v) {
	int64_t maxim = v[0], indice = 0;
	for (int i = 0; i < v.size() - 1; i++) {
		if (v[i] < v[i + 1] && maxim < v[i + 1]) {
			maxim = v[i + 1];
			indice = i + 1;

		}
		else if (v[i] > v[i + 1] && maxim < v[i]) {
			maxim = v[i];
			indice = i;
		}
	}

	return maxim;
}

int maxim(vector<int64_t> v) {
	int64_t m = v[0];
	for (auto el : v) {
		m = max(el, m);
	}
	return m;
}

vector<int64_t> generateRandomVector(int64_t n, int64_t left, int64_t right) {
	srand(time(NULL));

	int64_t space = right - left;
	vector <int64_t> v;
	for (int i = 0; i < n; i++) {
		int64_t el = rand() % space + left;
		v.push_back(el);
	}
	return v;
}

int64_t maxVector(vector<int64_t> a) {
	int64_t m = a[0];
	for (int i = 1; i < a.size(); i++) {
		m = max(a[i], m);
	}
	return m;
}

int64_t maximIndiceVector(vector<int64_t> a) {
	int64_t m = a[0];
	int indice = 0;
	for (int i = 1; i < a.size(); i++) {
		if (a[i] > m) {
			m = a[i];
			indice = i;
		}
	}
	return indice;
}

int gcd(int a, int b) {
	return b ? gcd(b, a % b) : a;
}



int main()
{   
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
	int64_t n, numerePrime;
	fin >> n;
	vector <bool> estePrim(n+1, true);
	numerePrime = 0;
	for (int i = 2; i <= n; i++) {
		if (estePrim[i] == true) {
			numerePrime++;
			for (int j = i*2; j <= n; j += i) {
				estePrim[j] = false;
			}
		}
	}
	fout << numerePrime;
}