#include <iostream>

#include <fstream>

using namespace std;

ifstream fin("ciur.in");

ofstream fout("ciur.out");

bool fv[2000005];



int main() {

    int n, nr_prime = 0;

    fin >> n;

    for (int i = 2; i * i <= n; i += 2) {

        for (int j = i * i; j <= n; j += i) {

            fv[j] = 1;

        }

        if (i == 2)

            --i;

    }

    for (int i = 2; i <= n; ++i)

        if (fv[i] == 0)

            ++nr_prime;

    fout << nr_prime;

    return 0;
}