#include <fstream>
#include <bitset>

using namespace std;

const int NMAX = 2e6;

bitset <1+NMAX> c;
//bool c[1+NMAX];

int main()
{
    ifstream in("ciur.in");
    ofstream out("ciur.out");
    int n;
    in >> n;
    in.close();
    for (int i = 2; i * i <= n; i++)
    {
        if (!c[i])
        {
            for (int j = i * i; j <= n; j += i)
            {
                c[j] = true;
            }
        }
    }
    int nr = 0;
    for (int i = 2; i <= n; i++)
    {
        if (!c[i])
        {
            nr++;
        }
    }
    out << nr;
    out.close();
    return 0;
}