#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5;
bool iscomp[maxn + 5], vis[maxn + 5];
void prime_table(int n) {
  for (int i = 2; i * i <= n; i++) {
    if (iscomp[i]) continue;
    for (int j = i * i; j <= n; j += i) iscomp[j] = 1;
  }
}
int main() {
  int n;
  scanf("%d", &n);
  prime_table(n);
  vector<int> g;
  vector<pair<int, int> > ans;
  for (int i = n / 2; i > 1; i--) {
    if (iscomp[i]) continue;
    g.clear();
    for (int j = i; j <= n; j += i) {
      if (vis[j] == 0) g.push_back(j);
    }
    if (g.size() & 1) swap(g[1], g[g.size() - 1]);
    for (int i = 0; i < g.size() - 1; i += 2) {
      ans.push_back(make_pair(g[i], g[i + 1]));
      vis[g[i]] = vis[g[i + 1]] = 1;
    }
  }
  printf("%lu\n", ans.size());
  for (int i = 0; i < ans.size(); i++)
    printf("%d %d\n", ans[i].first, ans[i].second);
  return 0;
}
