// PR Bab 06, soal 2 -- pembahasan.

#include <iostream>
using namespace std;

bool prima(long long n) {
    if (n < 2) return false;
    for (long long i = 2; i * i <= n; i++) {
        if (n % i == 0) return false;
    }
    return true;
}

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

    int banyak = 0;
    for (int i = 2; i <= n; i++) {
        if (prima(i)) banyak++;
    }

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