#include <bits/stdc++.h>
using namespace std;
int a[111111];
int b[111111];
int main() {
  int n, i, j;
  vector<pair<int, int> > v;
  scanf("%d", &n);
  a[0] = a[1] = 1;
  for (i = 2; i <= n; i++) {
    if (a[i] == 0) {
      for (j = i * 2; j <= n; j += i) a[j] = 1;
    }
  }
  for (i = n / 2; i > 0; i--) {
    if (a[i] == 0) {
      vector<int> w;
      for (j = i; j <= n; j += i) {
        if (b[j] == 0) w.push_back(j);
      }
      if (w.size() % 2 == 0) {
        for (j = 0; j < w.size(); j += 2) {
          v.push_back(make_pair(w[j], w[j + 1]));
          b[w[j]] = b[w[j + 1]] = 1;
        }
      } else {
        for (j = 0; j < w.size(); j++) {
          if (w[j] % 2 == 0) {
            swap(w[j], w.back());
            break;
          }
        }
        for (j = 0; j < w.size() - 1; j += 2) {
          v.push_back(make_pair(w[j], w[j + 1]));
          b[w[j]] = b[w[j + 1]] = 1;
        }
      }
    }
  }
  printf("%d\n", v.size());
  for (i = 0; i < v.size(); i++) printf("%d %d\n", v[i].first, v[i].second);
  return 0;
}
