#include <bits/stdc++.h>
using namespace std;
const int MAX = 1e5 + 2;
int prime[MAX], done[MAX];
int main() {
  int n;
  scanf("%d", &n);
  vector<int> primes, rem, temp;
  for (int i = 2; i <= n; i++) {
    if (!prime[i]) {
      primes.push_back(i);
      for (int j = i + i; j <= n; j += i) {
        prime[j] = 1;
      }
    }
  }
  reverse(primes.begin(), primes.end());
  vector<pair<int, int> > ans;
  for (int j = 0; j < primes.size(); j++) {
    int PRIME = primes[j];
    if (PRIME > n / 2) continue;
    temp.clear();
    for (int extra = PRIME; extra <= n; extra += PRIME)
      if (!done[extra]) {
        temp.push_back(extra);
        done[extra] = 1;
      }
    if (temp.size() == 1) {
      if (PRIME == 2) rem.push_back(PRIME);
      continue;
    }
    int i = temp.size();
    for (i = temp.size() - 1; i >= 1;) {
      ans.push_back(pair<int, int>(temp[i], temp[i - 1]));
      i -= 2;
    }
    if (i == 0) {
      rem.push_back(PRIME * 2);
      ans[ans.size() - 1].second = PRIME;
    }
  }
  for (int i = rem.size() - 1; i >= 1;) {
    ans.push_back(pair<int, int>(rem[i], rem[i - 1]));
    i -= 2;
  }
  cout << ans.size() << endl;
  for (int i = 0; i < ans.size(); i++)
    printf("%d %d\n", ans[i].first, ans[i].second);
  return 0;
}
