#include <iostream>
#include <math.h>
#include <fstream>

using namespace std;

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

int main()
{
    int n, r = 0;
    f >> n;
    for(int i = 2; i <= n; i++){
        int ok = 1;
        for(int d = 2; d <= sqrt(i); d++)
            if(i % d == 0)
                ok = 0;
            if(ok)
                r++;
    }

    g << r;

    return 0;
}