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

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n, i, t, j, gasit = 1, k, nr = 0;
    f >> n;
    for(i=2;i<=n;i++)
    {
        t=i;
        gasit = 1;
        if((t%2==0)&&(t!=2)) gasit = 0;
        else
        {
            for(k=3;k<=t/2;k+=2)
            {
                if(t%k==0) gasit = 0;
            }
        }
        if (gasit==1) nr++;
    }
    g << nr;
    f.close();
    g.close();
    return 0;
}