#include <fstream>
using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
bool ciur[2000001]; int n, k = 1;
int main()
{
    in >> n;
    for (int i = 2; i <= n; i += 2) ciur[i] = 1;
    for (int i = 3; i <= n; i += 2)
        if (!ciur[i])
        {
            k++;
            for (int j = i * i; j <= n; j += i << 1) ciur[j] = 1;
        }
    out << k << '\n';
    out.close(); return 0;
}