#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int main()
{
    int n, r = 0, i, i2;
    bool prim;
    fin >> n;
    for(i = 2; i<=n; i++)
    {
        prim = true;
        for(i2 = 2; i2<=i/2; i2++)
        {
            if(i % i2 == 0)
            {
                prim = false;
                break;
            }
        }
        if(prim == true)r++;
    }
    fout << r;
    return 0;
}