#include <fstream>

using namespace std;

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

    int n, nrCount = 0;
    fin >> n;
    fin.close();
    bool *nr = new bool[n+1];
    for (int i = 0; i <= n; ++i) {
        nr[i] = true;
    }

    for (int i = 2; i <= n; ++i) {
        if (nr[i] == true) {
            for (int j = i+i; j <= n; j += i) {
                nr[j] = false;
            }
            nrCount++;
        }
    }

    fout << nrCount << "\n";
    fout.close();

    return 0;
}