#include <bits/stdc++.h>
using namespace std;
long long int n, m, ar[1000005], sum, mark[1000005], prime[1000005];
vector<long long int> v, ans;
void sieve(int x) {
  for (int i = x; i <= n; i += x) {
    if (mark[i]) continue;
    prime[i] = 1;
    v.push_back(i);
  }
}
int main() {
  cin.tie(0);
  cout.tie(0);
  ios_base::sync_with_stdio(false);
  cin >> n;
  sieve(2);
  v.clear();
  for (int i = 3; i <= n / 2; i++) {
    if (prime[i]) continue;
    sieve(i);
    for (int j = 0; j < v.size(); j++) {
      if (v.size() % 2 == 1 && v[j] == i * 2) {
        continue;
      }
      mark[v[j]]++;
      ans.push_back(v[j]);
    }
    v.clear();
  }
  sieve(2);
  for (int j = 0; j < v.size() - v.size() % 2; j++) {
    mark[v[j]]++;
    ans.push_back(v[j]);
  }
  cout << ans.size() / 2 << "\n";
  for (int i = 0; i < ans.size(); i++) {
    cout << ans[i] << " ";
    if (i % 2 == 1) cout << "\n";
  }
}
