#include <fstream>

using namespace std;

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

int v[2000000], n, nr;

int main() {
    in >> n;
    for (int i = 2; i <= n; i++)
        if (!v[i]) {
            nr++;
            for (int j = 2 * i; j <= n; j += i)
                v[j] = 1;
        }
    out << nr;
    return 0;
}