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

using namespace std;

bool c[2000000];

int main()
{

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

    int x, p = 0;
    i >> x;

    for(int a = 2; a < x; a++)
    {
        if(!c[a])
        {
            p++;
            int t = a;

            for(int b = t*t; b < x-t; b = b + t)
            {
                c[b] = true;
            }
        }
    }

    o << p;

    return 0;
}