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

using namespace std;

int main()
{

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

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

    bool c[x];
    memset (c,true,x);

    for(int a = 0; a < x; a++)
    {
        if(a == 0)
        {
            continue;
        }

        if(c[a])
        {
            p++;
            int t = a+1;

            for(int b = t*t; b <= x; b = b + t)
            {
                c[b-1] = false;
            }
        }
    }

    o << p;

    return 0;
}