#include <bits/stdc++.h>
using namespace std;
const int N = 101000;
int n, isp[N], vis[N];
vector<pair<int, int> > ans;
vector<int> vec;
int main() {
  scanf("%d", &n);
  if (n <= 3) return puts("0"), 0;
  for (int i = 2; i <= n; i++)
    if (!isp[i]) {
      for (int j = i + i; j <= n; j += i) isp[j] = 1;
    }
  for (int i = 2; i <= n; i++)
    if (1ll * i * i > n && isp[i] == 0 && i * 2 <= n) {
      ans.push_back(make_pair(i, i * 2));
      vis[i] = vis[i * 2] = 1;
    }
  for (int i = n; i >= 2; i--)
    if (1ll * i * i <= n && isp[i] == 0) {
      vec.clear();
      for (int j = i; j <= n; j += i)
        if (!vis[j]) vec.push_back(j);
      if (vec.size() % 2 == 0) {
        for (int j = 0; j < vec.size(); j += 2) {
          int u = vec[j], v = vec[j + 1];
          ans.push_back(make_pair(u, v));
          vis[u] = vis[v] = 1;
        }
      } else {
        int u = vec[0], v = vec[2];
        ans.push_back(make_pair(u, v));
        vis[u] = vis[v] = 1;
        for (int j = 3; j < vec.size(); j += 2) {
          u = vec[j], v = vec[j + 1];
          ans.push_back(make_pair(u, v));
          vis[u] = vis[v] = 1;
        }
      }
    }
  printf("%d\n", ans.size());
  for (int i = 0; i < ans.size(); i++)
    printf("%d %d\n", ans[i].first, ans[i].second);
}
