#include <fstream>
const std::string programName = "ciur";
std::ifstream f(programName + ".in");
std::ofstream g(programName + ".out");
bool prim(int);
int main() {
    int N;
    f >> N;
    int counter = 0;
    for (int i = 2; i <= N; ++i)
        if (prim(i))
            ++counter;
    g << counter;
    return 0x0;
}
bool prim(int N) {
    for (int i = 2; i * i <= N; ++i)
        if (!(N % i))
            return false;
    return true;
}