#include <bits/stdc++.h>
using namespace std;
int n;
bool vis[100005], used[100005];
vector<int> pri;
vector<pair<int, int> > ans;
int main() {
  cin >> n;
  for (int i = 2; i <= n; i++) {
    if (vis[i] == 0) {
      pri.push_back(i);
      for (int j = i; j <= n; j += i) vis[j] = 1;
    }
  }
  for (int i = pri.size() - 1; i >= 0; i--) {
    vector<int> v;
    for (int j = pri[i]; j <= n; j += pri[i])
      if (used[j] == 0) v.push_back(j);
    if (v.size() == 1) continue;
    if (v.size() % 2 == 1) swap(v[1], v[v.size() - 1]);
    for (int i = 0; i < v.size() - 1; i += 2) {
      ans.push_back(make_pair(v[i], v[i + 1]));
      used[v[i]] = 1;
      used[v[i + 1]] = 1;
    }
  }
  cout << ans.size() << '\n';
  for (int i = 0; i < ans.size(); i++)
    cout << ans[i].first << ' ' << ans[i].second << '\n';
  return 0;
}
