#include <fstream>

using namespace std;

int main() {
    ifstream f("ciur.in");
    ofstream g("ciur.out");

    int n;

    f>> n;
    bool check[2000005];

    int result = 0;
    for (int i = 2; i <= n; i++) {
        if (check[i] == 0) {
            result += 1;
            for (int j = i; j <= n ; j+= i) {
                check[j] = true;
            }
        }
    }

    g<< result;

    return 0;
}