#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 1e5;
int n;
bool isPrime[MAX_N + 1];
vector<int> primes;
vector<int> v[MAX_N];
int main() {
  cin >> n;
  for (int i = 2; i <= n; i++) isPrime[i] = true;
  for (int i = 2; i * i <= n; i++)
    if (isPrime[i]) {
      for (int j = i * 2; j <= n; j += i) isPrime[j] = false;
    }
  for (int i = 1; i <= n; i++)
    if (isPrime[i]) primes.push_back(i);
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j < int(primes.size()); j++)
      if (i % primes[j] == 0) {
        v[j].push_back(i);
        break;
      }
  }
  for (int i = 1; i < primes.size(); i++) {
    if (v[i].size() % 2 == 1) {
      auto it = find(v[0].begin(), v[0].end(), 2 * primes[i]);
      if (it != v[0].end()) {
        v[0].erase(it);
        v[i].push_back(2 * primes[i]);
      }
    }
  }
  int c = 0;
  for (int i = 0; i < int(primes.size()); i++) c += v[i].size() / 2;
  cout << c << endl;
  for (int i = 0; i < int(primes.size()); i++) {
    for (int j = 0; j < int(v[i].size() / 2); j++) {
      cout << v[i][2 * j] << " " << v[i][2 * j + 1] << endl;
    }
  }
}
