#include <fstream>
using namespace std;

ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

bool a [2000001];
int n, contor;

int main()
{
    fin >> n;
    for (int i = 2; i <= n; ++i)
    {
        if (!a[i])
            for (int j = 2; i * j <= n; ++j)
                a[i * j] = true;
    }
    for (int i = 2; i <= n; ++i)
        if (!a[i])
            contor++;
    fout << contor;
}