#include <fstream>

using namespace std;

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

const int MAX_N = 2000000;

int n;
bool used[MAX_N + 1];

void ciur() {
  for (int i = 2; i <= MAX_N; ++i) {
    if (!used[i]) {
      for (int j = i + i; j <= MAX_N; j += i) {
        used[j] = true;
      }
    }
  }
}

int main() {
  ciur();
  fin >> n;

  int sol = 0;
  for (int i = 2; i <= n; ++i) {
    if (!used[i]) {
      ++sol;
    }
  }

  fout << sol << '\n';
  return 0;
}