#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    ifstream fin ("ciur.in");
    ofstream fout ("ciur.out");
    int n, i, j, s=0, asf;
    fin>>n;

    for (i=2; i<n; i++)
    {
        asf=0;

        for (j=2; j<=i/2; j++)
            if (i%j==0)
                asf=1;

        if (asf==0)
            s++;
    }
    fout<<s;
    return 0;
}