#include <iostream>
#include <fstream>
using namespace std;

int primality_of_numbers[2000001];

void eratostene(int n, int &number_of_prime_numbers) {
    for (int i = 2; i <= n; i++) {
        if (primality_of_numbers[i] == 0) {
            ++number_of_prime_numbers;
            for (int j = 2; j * i <= n; j++) {
                ++primality_of_numbers[j * i];
            }
        }
    }
}

int main() {
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n, c = 0;
    fin >> n;
    eratostene(n, c);
    fout << c;
    return 0;
}