#include <bits/stdc++.h>
using namespace std;
const int maxn = 100010;
int prime[maxn], cnt, vis[maxn];
void init_prim() {
  memset(vis, 0, sizeof(vis));
  cnt = 0;
  for (int i = 2; i <= 100000; ++i) {
    if (!vis[i]) prime[cnt++] = i;
    for (int j = 0; (j < cnt) && (i * prime[j] <= 100000); ++j) {
      vis[i * prime[j]] = 1;
      if (i % prime[j] == 0) break;
    }
  }
}
int flag[maxn], ans;
int save[maxn][2], pre, cache;
int main() {
  int n;
  init_prim();
  scanf("%d", &n);
  memset(flag, 0, sizeof(flag));
  ans = 0;
  int temp;
  for (int i = 1; i < cnt; i++) {
    if (prime[i] > n / 2) break;
    temp = 0;
    int fac = 1;
    while (fac * prime[i] <= n) {
      if (!flag[fac * prime[i]]) {
        flag[fac * prime[i]] = 1;
        temp++;
        if (temp > 2 && temp % 2 == 0) {
          save[ans][0] = fac * prime[i];
          save[ans][1] = cache;
          ans++;
        }
        cache = fac * prime[i];
      }
      fac++;
    }
    if (temp % 2 == 1) {
      flag[2 * prime[i]] = 0;
      temp--;
      save[ans][0] = prime[i];
      save[ans][1] = cache;
      ans++;
    } else {
      save[ans][0] = prime[i];
      save[ans][1] = 2 * prime[i];
      ans++;
    }
  }
  temp = 0;
  for (int i = 2; i <= n; i += 2) {
    if (!flag[i]) {
      flag[i] = 1;
      temp++;
      if (temp % 2 == 0) {
        save[ans][0] = i;
        save[ans][1] = cache;
        ans++;
      }
      cache = i;
    }
  }
  cout << ans << endl;
  for (int i = 0; i < ans; i++) {
    printf("%d %d\n", save[i][0], save[i][1]);
  }
  return 0;
}
