#include <bits/stdc++.h>
using namespace std;
const int M = 1000 * 100 + 4, Inf = 1e9 + 10;
bool mk[M];
vector<pair<int, int> > ans;
bool prime(int n) {
  bool b = 1;
  for (int i = 2; i * i <= n && b; i++)
    if (!(n % i)) b = 0;
  return b;
}
int main() {
  ios::sync_with_stdio(false);
  int n;
  cin >> n;
  int x = 0;
  for (int i = n; i > 1; i--, x = 0)
    if (prime(i)) {
      if (!mk[i]) x = i;
      int j;
      for (j = i * 3; j <= n; j += i)
        if (!mk[j]) {
          if (!x)
            x = j;
          else {
            mk[x] = mk[j] = 1;
            ans.push_back(make_pair(x, j));
            x = 0;
          }
        }
      if (x && 2 * i <= n)
        ans.push_back(make_pair(x, 2 * i)), mk[2 * i] = mk[x] = 1;
    }
  cout << ans.size() << endl;
  for (int i = 0; i < ans.size(); i++)
    cout << ans[i].first << " " << ans[i].second << endl;
  return 0;
}
