#include <fstream>

using namespace std;

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

unsigned Ciur(int x) {
    unsigned nr = 0;

    for (int i = 2; i <= x; i++) {
        unsigned counter = 0;

        for (int j = 2; j <= i / 2; j++) {
            if (i % j == 0)
                counter++;
        }

        if (counter == 0)
            nr ++;
    }

    return nr;
}

int main() {
    unsigned N;
    fin >> N;
    fout << Ciur(N);
}