#include <iostream>
#include <fstream>
using namespace std;

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

int nr,n,i,ok;

int main()
{
    f >> n;
    for(i=1;i<=n;i++)
    {
        ok = 1;
        for(int j=2;j<=i/2;j++)
            if(i%j==0)
                ok = 0;
        if(ok==1)
            nr++;
    }
    g << nr;
    return 0;
}