#include <bits/stdc++.h>
using namespace std;
template <class T1, class T2>
ostream& operator<<(ostream& out, pair<T1, T2> p) {
  out << p.first << ' ' << p.second;
  return out;
}
template <class T1, class T2>
istream& operator>>(istream& in, pair<T1, T2>& p) {
  in >> p.first >> p.second;
  return in;
}
template <class T>
istream& operator>>(istream& in, vector<T>& v) {
  for (auto& x : v) in >> x;
  return in;
}
template <class T>
ostream& operator<<(ostream& out, vector<vector<T>>& v) {
  for (auto& x : v) out << x << '\n';
  return out;
}
template <class T>
ostream& operator<<(ostream& out, vector<T>& v) {
  for (auto x : v) out << x << ' ';
  return out;
}
const int N = 100005;
int n;
vector<int> p(N, 0), used(N, 0), vec;
vector<pair<int, int>> ans;
void solve() {
  cin >> n;
  for (int i = 2; i < N; i++) {
    if (p[i] == 0) {
      for (int j = 2 * i; j < N; j += i) {
        p[j] = 1;
      }
    }
  }
  for (int i = 3; i * 2 <= n; i++) {
    if (p[i] == 0) {
      vec.clear();
      for (int j = i; j <= n; j += i) {
        if (used[j] == 0) vec.push_back(j);
      }
      if (vec.size() % 2) {
        vec.erase(vec.begin() + 1);
      }
      for (int j = 0; j < vec.size(); j += 2) {
        ans.push_back({vec[j], vec[j + 1]});
        used[vec[j]] = 1;
        used[vec[j + 1]] = 1;
      }
    }
  }
  vec.clear();
  for (int j = 2; j <= n; j++) {
    if (used[j] == 0 && j % 2 == 0) vec.push_back(j);
  }
  for (int j = 0; j + 1 < vec.size(); j += 2) {
    ans.push_back(make_pair(vec[j], vec[j + 1]));
    used[vec[j]] = used[vec[j + 1]] = 1;
  }
  cout << ans.size() << "\n";
  for (auto i : ans) {
    cout << i << "\n";
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int t;
  t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
