#include <bits/stdc++.h>
using namespace std;
long long int mod = 1e9 + 7;
int inf = 2e9;
long long int linf = 1000ll * 1000 * 1000 * 1000 * 1000 * 1000;
const int maxn = 1e5 + 200;
vector<int> tmp;
vector<pair<long long int, long long int> > ans;
int lp[maxn];
int match[maxn];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  for (int i = 2; i <= n; i++) {
    if (!lp[i]) {
      for (int j = i; j <= n; j += i) {
        if (!lp[j]) {
          lp[j] = i;
        }
      }
    }
  }
  for (int i = n / 2; i >= 2; i--) {
    if (lp[i] == i) {
      tmp.clear();
      for (int j = i; j <= n; j += i) {
        if (!match[j]) {
          tmp.push_back(j);
        }
      }
      if (tmp.size() % 2 == 1) {
        match[tmp[0]] = tmp[2];
        match[tmp[2]] = tmp[0];
        ans.push_back({tmp[0], tmp[2]});
        for (int i = 3; i < tmp.size(); i += 2) {
          match[tmp[i]] = tmp[i + 1];
          match[tmp[i + 1]] = tmp[i];
          ans.push_back({tmp[i], tmp[i + 1]});
        }
      } else {
        for (int i = 0; i < tmp.size(); i += 2) {
          match[tmp[i]] = tmp[i + 1];
          match[tmp[i + 1]] = tmp[i];
          ans.push_back({tmp[i], tmp[i + 1]});
        }
      }
    }
  }
  cout << ans.size() << "\n";
  for (pair<long long int, long long int> P : ans) {
    cout << P.first << " " << P.second << "\n";
  }
  return 0;
}
