#include <iostream>
#include <fstream>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <vector>
#include <algorithm>
#include <cmath>
#include <chrono>

using namespace std;

int main(int argc, const char * argv[]) {
    
    ios::sync_with_stdio(false);
    cin.tie(0);
    
    int n;
    while (cin >> n) {
        if (n == 1) {
            cout << 0 << endl;
            continue;
        }
        
        vector<bool> is_prime(n + 1, true);
        is_prime[0] = false; is_prime[1] = false;
        for (int i = 2; i <= n; i++) {
            if (is_prime[i]) {
                for (int j = 2 * i; j <= n; j += i) {
                    is_prime[j] = false;
                }
            }
        }
        
        int ans = 0;
        for (int i = 0; i <= n; i++) {
            if (is_prime[i]) ans++;
        }
        cout << ans << endl;
    }
    
    return 0;
}

