#include <iostream>
#include <fstream>

using namespace std;

int main()
{
    ifstream fin ("ciur2.in");
    ofstream fout ("ciur2.out");
    int n, i, j, s=1, asf, v[500];
    fin>>n;
    v[0]=2;
    for (i=3; i<=n; i++)
    {
        asf=0;
        for (j=2; j<s; j++)
            if (i%j==0)
                asf=1;

        if (asf==0)
        {
            v[s]=i;
            s++;
        }
    }
    fout<<s-1;
    return 0;
}