#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 20;
const long long inf = 1e10;
vector<pair<int, int>> ans;
bool vis[N], matched[N];
int main() {
  ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  int n;
  cin >> n;
  for (int i = 2; i * i <= n; i++) {
    if (!vis[i])
      for (int j = i * i; j <= n; j += i) vis[j] = true;
  }
  for (int i = n; i > 1; i--) {
    if (!vis[i]) {
      vector<int> tmp;
      for (int j = i; j <= n; j += i)
        if (!matched[j]) tmp.push_back(j);
      bool e = false;
      int pos = 0;
      if (tmp.size() % 2) {
        if (tmp.size() > 2)
          ans.push_back({tmp[0], tmp[2]}),
              matched[tmp[0]] = matched[tmp[2]] = true;
        pos = 3;
      }
      for (int j = pos; j < tmp.size(); j += 2)
        ans.push_back({tmp[j], tmp[j + 1]}),
            matched[tmp[j]] = matched[tmp[j + 1]] = true;
    }
  }
  cout << ans.size() << endl;
  for (auto u : ans) cout << u.first << " " << u.second << endl;
  return 0;
}
