#include <fstream>

using namespace std;

ifstream cin ("ciur.in");
ofstream cout ("ciur.out");

const int N = 2e6 + 5;

int n, cnt;
bool prim[N];

int main()  {
    cin >> n;
    for (int i = 2; i <= n; ++i)
        prim[i] = true;
    for (int i = 2; i <= n; ++i)    {
        if (prim[i])    {
            ++cnt;
            for (int j = i * i; j <= n; j += i) {
                prim[j] = false;
            }
        }
    }
    cout << cnt;
    return 0;
}