// ciur.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool v[2000001];
int main()
{
    int n, ct = 0;
    in >> n;
    for (int i = 2; i * i <= n; i++) {
        if (v[i] == 0) {
            for (int j = i * 2; j <= n; j += i) {
                v[j] = 1;
            }
        }
    }
    for (int i = 2; i <= n; i++) {
        if (v[i] == 0) {
            ct++;
        }
    }
    out << ct;

}

// Run program: Ctrl + F5 or Debug > Start Without Debugging menu
// Debug program: F5 or Debug > Start Debugging menu

// Tips for Getting Started: 
//   1. Use the Solution Explorer window to add/manage files
//   2. Use the Team Explorer window to connect to source control
//   3. Use the Output window to see build output and other messages
//   4. Use the Error List window to view errors
//   5. Go to Project > Add New Item to create new code files, or Project > Add Existing Item to add existing code files to the project
//   6. In the future, to open this project again, go to File > Open > Project and select the .sln file