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

bool is_prime[2000001];

int main() {
	ifstream cin("ciur.in");
  	ofstream cout("ciur.out");
    int n;
    cin >> n;
    for (int i = 2; i * i <= n; ++i) {
        for (int j = i; i * j <= n && !is_prime[i]; ++j) {
            is_prime[i * j] = true;
        }
    }
    int rez = 0;
    for (int i = 2; i <= n; ++i) {
        if (!is_prime[i]) {
            ++rez;
        }
    }
    cout << rez;
  	cout.close();
    return 0;
}