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

using namespace std;

int main()
{
    int n, i=3, c, k=0, v[299999];

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

    f>>n;
    if (n>=2)
        k++;

    while (i <= n)
    {
        c=2;
        v[i]=0;
        while (c<=sqrt(i))
        {
            if (i%c==0)
                v[i] = 1;
            c++;
        }

        if (v[i] == 0)
            k++;

        i+=2;
    }

    g<<k;



}