#include <fstream>
using namespace std;
bool compus[2000001];

int main() {
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n, i, j, nr = 0;
    fin >> n;

    for (i = 2; i <= n; i++) {
        if (compus[i] == false) {
            //deci numarul i este prim
            nr++;
            for (j = 2 * i; j <= n; j += i) {
                compus[j] = true;
            }
        }
    }

    fout << nr;
    return 0;
}