#include <bits/stdc++.h>
using namespace std;

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

int main() {
    int N;
    fin >> N;

    // toate nr prime
    vector<bool> prim(N + 1, true);
    prim[0] = prim[1] = false;

    for (int i = 2; i * i <= N; i++) {
        if (prim[i]) {
            //eliminare mltiplii i
            for (int j = i * i; j <= N; j += i) {
                prim[j] = false;
            }
        }
    }
    int x=0;
    for (int i = 2; i <= N; i++) {
        if (prim[i]) {
            x++;
        }
    }
    fout << x;

    return 0;
}