#include <iostream>
#include <fstream>

using namespace std;

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

int n, v[2000001], nr_prime;

int main() {
    fin >> n;
    for (int i = 2; i * i <= n; ++i) {
        if (v[i] == 0) {
            ++nr_prime;
            for (int j = i * 2; j <= n; j += i)
                v[j] = 1;
        }
    }
    fout << nr_prime;
}