#include <iostream>
#include <fstream>
using namespace std;

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

int main() {
    bool prim;
    int n, i, nr = 2, raspuns = 0;
    fin >> n;
    if(n < 2) {
        fout << 0;
    } else {
        while(nr <= n) {
            prim = true;
            for(i = 2; i <= nr / 2; ++i) {
                if(nr % i == 0)
                    prim = false;
            }
            ++nr;
            if(prim)
                ++raspuns;
        }
    }

    fout << raspuns;

    return 0;
}