#include <bits/stdc++.h>
using namespace std;
int main(void) {
  ios ::sync_with_stdio(0);
  cin.tie(0);
  set<int> s;
  int n;
  cin >> n;
  vector<bool> prime(n + 1, true), available(n + 1, true);
  vector<int> ans;
  prime[0] = prime[1] = false;
  for (int i = 2; i * i <= n; ++i) {
    if (prime[i]) {
      for (int j = i * i; j <= n; j += i) {
        prime[j] = false;
      }
    }
  }
  for (int i = 3; 2 * i <= n; ++i) {
    s.clear();
    if (prime[i]) {
      for (int j = i; j <= n; j += i) {
        if (available[j]) {
          s.insert(j);
          available[j] = false;
        }
      }
    }
    if (s.size() % 2 == 1) {
      s.erase(2 * i);
      available[2 * i] = true;
    }
    for (int c : s) {
      ans.push_back(c);
    }
  }
  for (int i = 2; i <= n; i += 2) {
    if (available[i]) {
      ans.emplace_back(i);
    }
  }
  if (ans.size() % 2 == 1) {
    ans.pop_back();
  }
  cout << ans.size() / 2 << endl;
  for (int i = 0; i <= (int)ans.size() - 2; i += 2) {
    cout << ans[i] << " " << ans[i + 1] << "\n";
  }
  return 0;
}
