#include <fstream>

using namespace std;

bool t[2000003];

int main()
{
    int i, j, contor, n;
    ifstream fin("ciur.in");
    fin >> n;
    fin.close();

    for (i = 3; i * i <= n; i += 2)
        if (t[i] == false)
            for (j = i * i; j <= n; j = j + 2 * i)
                t[j] = true;
    contor = 1;
    for (i = 3; i <= n; i += 2)
        if (t[i] == false) contor++;

    ofstream fout("ciur.out");
    fout << contor << "\n";
    fout.close();
    return 0;
}