#include <iostream>
#include <fstream>
#include <cmath>

using namespace std;

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

int main() {
    int n, p=0;
    bool m[2000000];
    in>>n;
    for (int i=2; i<=n; i++) {
        m[i] = true;
        for (int y=2; (float)y<=sqrt(i); y++) {
            if (i%y == 0) m[i] = false;
        }
    }
    for (int i=2; i<=n; i++) {
        if (m[i] == true) p++;
    }
    out<<p;
}