#include <fstream>
#include <cmath>
using namespace std;

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

int main() {
    fin.tie(0);
    ios::sync_with_stdio(0);
    int n;
    fin >> n;

    bool isNotPrime[n + 1] = {false};
    int margin = sqrt(n);
    for (int i = 2; i <= margin; i++)
        for (int j = 2; i * j <= n; j++)
            isNotPrime[i * j] = true;

    int nr = 0;
    for (int i = 2; i <= n; i++)
        if (!isNotPrime[i])
            nr++;
    fout << nr;

    return 0;
}