#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e5 + 10, mod = 1e9 + 7;
int T, p[maxn], tot, f[maxn], g[maxn];
vector<int> ve[maxn];
vector<pair<int, int> > ans;
void sieve(int n) {
  tot = 0, f[1] = 1;
  for (int i = 1; i <= n; i++) g[i] = f[i] = 0, ve[i].clear();
  for (int i = 2; i <= n; i++) {
    if (!f[i]) p[++tot] = g[i] = i, ve[i].push_back(i);
    for (int j = 1; j <= tot && i * p[j] <= n; j++) {
      f[i * p[j]] = 1, g[i * p[j]] = g[i], ve[g[i]].push_back(i * p[j]);
      if (i % p[j] == 0) break;
    }
  }
}
int main() {
  int n;
  scanf("%d", &n);
  sieve(n);
  while (p[tot] * 2 > n) tot--;
  ans.clear();
  for (int i = tot; i >= 2; i--) {
    if (ve[p[i]].size() % 2) {
      ve[p[i]].erase(find(ve[p[i]].begin(), ve[p[i]].end(), p[i] * 2));
      ve[2].push_back(p[i] * 2);
    }
    for (int j = 0; j < ve[p[i]].size(); j += 2)
      ans.push_back(make_pair(ve[p[i]][j], ve[p[i]][j + 1]));
  }
  if (ve[2].size() % 2) ve[2].pop_back();
  for (int j = 0; j < ve[2].size(); j += 2)
    ans.push_back(make_pair(ve[2][j], ve[2][j + 1]));
  printf("%d\n", ans.size());
  for (auto p : ans) printf("%d %d\n", p.first, p.second);
  return 0;
}
