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

using namespace std;

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

int main()
{
    int n,i,ok,x,contor,d;
    f >>n;
    contor=0;
    for (i=1;i<=n;i++)
    {
        x=i;
        if (x<2)
        {
            ok=0;
        }
        else
        {
            ok=1;
            d=2;
            while (d<=sqrt(x) and ok==1)
            {
                if (x%d==0)
                {
                    ok=0;
                }
                else
                {
                    d++;
                }
            }
        }
        if (ok==1)
        {
            contor++;
        }
    }
    g <<contor;
    return 0;
}