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

int main()
{
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    int n, i, d, prim, app = 0;
    f >> n;
    for(i=1;i<=n;i++)
    {
        d=2;
        prim=1;
        while(d<=i/2)
        {
            if(i%d==0) prim=0;
            d++;
        }
        if(prim==1) app++;
    }
    g << app;
    f.close();
    g.close();
    return 0;
}