#include <fstream>

using namespace std;

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

int checkPrime(int x) {
    for (int i = 2; i <= x / 2; i++)
        if (x % i == 0)
            return 0;

    return 1;
}

int Ciur(int N) {
    int counter = 0;

    for (int i = 2; i <= N; i++) {
        if (checkPrime(i))
            counter++;
    }

    return counter;
}

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