#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n, num;
bool prime[2000005];

void get_prime(int i) {
    for (int j = 2 * i; j <= n; j += i) {
        prime[j] = true;
    }
}

int main() {
    fin >> n;
    for (int i = 2; i <= n; ++i) {
        if (!prime[i]) {
            ++num;
            get_prime(i);
        }
    }
    fout << num;
}