#include <fstream>
#include <bitset>

using namespace std;

const int N = 2e6;

int main() {
    bitset <N+1> c;
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n;
    fin >> n;
    for (int d = 2; d * d <= n; d++) {
        if (!c[d]) {
            for (int m = d * d; m <= n; m += d) {
                c[m] = 1;
            }
        }
    }
    int nr = 0;
    for (int i = 2; i <= n; i++) {
        if (!c[i]) {
            nr++;
        }
    }
    fout << nr << "\n";
    fin.close();
    fout.close();
    return 0;
}