#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  bool v[100005];
  vector<pair<int, int> > res;
  vector<int> t;
  cin >> n;
  for (int i = 2; i <= n; ++i) v[i] = false;
  for (int i = 3; i < n; i += 2) {
    if (!v[i]) {
      t.clear();
      for (int j = i; j <= n; j += i * 2) {
        if (!v[j]) t.push_back(j);
      }
      if ((t.size() % 2 == 1) && (i * 2 <= n)) t.push_back(i * 2);
      for (int j = 0; j + 1 < t.size(); j += 2) {
        res.push_back(make_pair(t[j], t[j + 1]));
        v[t[j]] = true;
        v[t[j + 1]] = true;
      }
    }
  }
  t.clear();
  for (int i = 2; i <= n; i += 2)
    if (!v[i]) t.push_back(i);
  for (int i = 0; i + 1 < t.size(); i += 2)
    res.push_back(make_pair(t[i], t[i + 1]));
  cout << res.size() << endl;
  for (int i = 0; i < res.size(); ++i)
    cout << res[i].first << " " << res[i].second << endl;
  return 0;
}
