#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
ifstream f ("ciur.in");
ofstream g ("ciur.out");
int main()
{
    int n,i,x,d,contor;
    bool prim;
    contor=0;
    f>>n;
    for (i=2;i<=n;i++)
    {
        prim=1;
        for (d=2;d<=sqrt(i);d++)
        {
            if (i%d==0)
            {
                prim=0;
                break;
            }
        }
        if (prim==1)
        {
            contor++;
        }
    }
    g<<contor;
    return 0;
}