#include <iostream>
#include <fstream>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

int v[2000001];

int main()
{
    int n, s = 0;
    f >> n;
    for (int i = 2; i < n; i++) {
        if (v[i] != 1) {
            for (int j = 2 * i; j <= n; j += i) {
                v[j] = 1;
            }
        }
    }
    for (int i = 2; i <= n; i++) {
        if (v[i] == 0) s++;
    }
    g << s;
    return 0;
}