#include <fstream>
std::ifstream fin("ciur.in");
std::ofstream fout("ciur.out");
const int NMAX = 2000001;
char sir[NMAX];
int n;
int main() {
  fin >> n;
  for (int i = 0; i <= n; i++)
    sir[i] = 0;
  sir[0] = sir[1] = 1;

  for (int i = 2; i * i <= n; ++i)
    if (sir[i] == 0)
      for (int j = 2; i * j <= n; ++j)
        sir[i * j] = 1;

  int total = 0;
  for (int i = 2; i <= n; ++i)
    if (sir[i] == 0)
      total++;
  fout << total;
  fin.close();
  fout.close();

  return 0;
}