#include <bits/stdc++.h>
using namespace std;
const int dx[9] = {0, 1, -1, 0, 0, -1, -1, 1, 1};
const int dy[9] = {0, 0, 0, -1, 1, -1, 1, -1, 1};
const double pi = acos(-1.0);
const int N = 1e5 + 100;
int n;
bool iszs[N], vis[N];
vector<int> v, v1;
vector<pair<int, int> > ans;
int main() {
  ios::sync_with_stdio(0), cin.tie(0);
  cin >> n;
  memset(iszs, 1, sizeof iszs);
  for (int i = 2; i <= n; i++) {
    if (iszs[i]) v.push_back(i);
    for (int j = 0; j <= (int)v.size() - 1; j++) {
      int t = v[j];
      if (i * t > n) break;
      iszs[i * t] = false;
      if (i % t == 0) break;
    }
  }
  for (int i = n / 2; i >= 2; i--)
    if (!vis[i] && iszs[i]) {
      v1.clear();
      for (int j = i; j <= n; j += i)
        if (!vis[j]) {
          v1.push_back(j);
        }
      int len = v1.size();
      if (len % 2 == 1) {
        swap(v1[1], v1[len - 1]);
      }
      for (int j = 0; j < len - 1; j += 2) {
        vis[v1[j]] = vis[v1[j + 1]] = 1;
        ans.push_back(make_pair(v1[j], v1[j + 1]));
      }
    }
  cout << (int)ans.size() << endl;
  for (int i = 0; i <= (int)ans.size() - 1; i++) {
    cout << ans[i].first << ' ' << ans[i].second << endl;
  }
  return 0;
}
