#include <iostream>
#include <fstream>

using namespace std;

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

bool ciur [2000001];
int main() {
    int n;
    in >> n;
    for (int i = 2; i * i <= n; i ++) {
        if (!ciur [i]) {
            for (int j = i * i; j <= n; j += i) {
                ciur [j] = true;
            }
        }
    }
    int prime = 0;
    for (int i = 2; i <= n; i ++) {
        if (!ciur [i])
            prime ++;
    }
    out << prime;
    return 0;
}