#include <bits/stdc++.h>

using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

int n;
int main() {

    in >> n;
    vector<bool> sieve(n + 1, 0);

    sieve[0] = sieve[1] = 1;
    int ans = 0;
    for (int i = 2; i <= n; i++) {
        if (sieve[i]) {
            continue;
        }

        ans++;
        for (int j = 2; i * j <= n; j++)
            sieve[i * j] = 1;
    }

    out << ans << '\n';
    return 0;
}