#include <iostream>
using namespace std;

const int N = 2e6;
bool prim[N + 1];

void Ciur(int n)
{
      for (int i = 2; i <= n; ++i)
            prim[i] = true;

      for (int i = 2; i * i <= n; ++i)
            if (prim[i])
                  for (int j = 2; i * j <= n; ++j)
                        prim[i * j] = false;
}

int main()
{
      Ciur(N);

      int n;
      cin >> n;
      int nr = 2, cnt = 0;
      while (nr <= n)
      {
            if (prim[nr])
                  cnt++;
            if (nr == 2)
                  nr++;
            else
                  nr += 2;
      }

      cout << cnt;
}