// Contoh Bab 07: saringan Eratosthenes.
//
// Compile:  g++ -std=c++17 -O2 -o saringan exercises/07/05-saringan.cpp
// Jalankan: ./saringan
// Contoh masukan: 1000000

#include <iostream>
using namespace std;

const int MAKS = 1000001;
bool coret[MAKS];

void saring(int n) {
    coret[0] = coret[1] = true;
    for (int i = 2; (long long)i * i <= n; i++) {
        if (!coret[i]) {
            for (int j = i * i; j <= n; j += i) coret[j] = true;
        }
    }
}

int main() {
    int n;
    cin >> n;

    saring(n);

    int banyak = 0;
    for (int i = 2; i <= n; i++) if (!coret[i]) banyak++;

    cout << banyak << "\n";
    return 0;
}