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

using namespace std;

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

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

    f>>n;
    if (n>=2)
    k++;
    for (i = 3; i <= n; i+=2)
    {
        v[i]=0;
        for (c=2; c<=sqrt(i); c++)
        if (i%c==0)
        v[i] = 1;


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

    g<<k;



}