#include <bits/stdc++.h>

using namespace std;

const int len = 2000005;
int n, cnt;
bool prime[len];

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    cin >> n;
    for (int i = 2; i <= n; i++)
        prime[i] = 1;
    for (int i = 2; i <= n; i++)
        if (prime[i]) {
            cnt++;
            for (int j = 2 * i; j <= n; j += i)
                prime[j] = 0;
        }

    cout << cnt;
}