#include <bits/stdc++.h>
using namespace std;
const int mx = 2000 * 100 + 10;
bool mark[mx], ans[mx], pr[mx];
vector<int> v;
vector<pair<int, int> > match;
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int n;
  cin >> n;
  for (int i = 2; i <= n; i++)
    if (!mark[i]) {
      pr[i] = 1;
      for (int j = i; j <= n; j += i) mark[j] = 1;
    }
  for (int i = n; i > 1; i--)
    if (pr[i]) {
      v.clear();
      for (int j = i; j <= n; j += i)
        if (!ans[j]) v.push_back(j), ans[j] = 1;
      if (v.size() == 1) continue;
      if (v.size() % 2) ans[v[1]] = 0, v.erase(v.begin() + 1);
      for (int j = 0; j < v.size(); j += 2) match.push_back({v[j], v[j + 1]});
    }
  cout << match.size() << "\n";
  for (auto now : match) cout << now.first << " " << now.second << "\n";
}
