#include <bits/stdc++.h>
using namespace std;
const int maxN = 100 * 1000 + 5;
vector<int> a[maxN];
int mark[maxN];
int main() {
  int n;
  cin >> n;
  for (int i = 3; i <= n / 2; i++)
    if (!mark[i])
      for (int j = i; j <= n; j += i)
        if (!mark[j]) a[i].push_back(j), mark[j] = 1;
  vector<pair<int, int> > ans;
  vector<int> r;
  memset(mark, 0, sizeof mark);
  for (int i = 3; i <= n / 2; i++) {
    if (a[i].size() & 1) {
      ans.push_back(make_pair(a[i][0], a[i][2]));
      mark[a[i][0]] = 1;
      mark[a[i][2]] = 1;
      for (int j = 3; j < a[i].size(); j += 2) {
        ans.push_back(make_pair(a[i][j], a[i][j + 1]));
        mark[a[i][j]] = mark[a[i][j + 1]] = 1;
      }
    } else
      for (int j = 0; j < a[i].size(); j += 2)
        ans.push_back(make_pair(a[i][j], a[i][j + 1])),
            mark[a[i][j]] = mark[a[i][j + 1]] = 1;
  }
  for (int i = 2; i <= n; i += 2)
    if (!mark[i]) r.push_back(i);
  for (int i = 0; i < (r.size() / 2) * 2; i += 2)
    ans.push_back(make_pair(r[i], r[i + 1]));
  cout << ans.size() << endl;
  for (auto u : ans) cout << u.first << ' ' << u.second << endl;
}
