#include <iostream>
#include <fstream>
#include <bitset>
using namespace std;

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

const int maxn = 2e6 + 5;
bitset <maxn> Sieve;
int n, ans;

int main() {
    ios_base :: sync_with_stdio(false);
    fin >> n;
    for (int i = 2; i <= n; i++) {
        if (Sieve[i] == false) {
            ans++;
            for (int j = i << 1; j <= n; j += i) {
                Sieve[j] = true;
            }
        }
    }
    fout << ans << "\n";
    return 0;
}