#include <fstream>

using namespace std;

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

    int n, nrCount = 1;
    fin >> n;
    fin.close();
    bool *nr = new bool[n/2+1];
    for (int i = 1; (i * 2) + 1 <= n; ++i) {
        nr[i] = true;
    }

    for (int i = 1; (i * i * 4) + (i * 4) + 1 <= n; ++i) {
        if (nr[i] == true) {
            for (int j = (i * i * 2) + (i * 2); (j * 2) + 1 <= n; j += (i * 2) + 1) {
                nr[j] = false;
            }
        }
    }

    for (int i = 1; (2 * i) + 1 <= n; ++i) {
        if (nr[i] == true) {
            nrCount++;
        }
    }

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

    return 0;
}