#include <bits/stdc++.h>
using namespace std;
int N;
int minp[100100];
int cnt[100100];
int rob[100100];
vector<int> cands[100100];
int main() {
  scanf("%d", &N);
  for (int i = 0; i <= N; i++) {
    minp[i] = -1;
    cnt[i] = 0;
    rob[i] = -1;
  }
  for (int i = 2; i <= N; i++)
    if (minp[i] == -1) {
      minp[i] = i;
      for (int j = i; j <= N; j += i)
        if (minp[j] == -1) minp[j] = i;
    }
  for (int i = 2; i <= N; i++) {
    cnt[minp[i]]++;
  }
  for (int i = 3; i <= N / 2; i++)
    if (i == minp[i]) {
      if (cnt[i] % 2 == 1) {
        rob[2 * i] = i;
        cnt[2]--;
      }
    }
  for (int i = 2; i <= N; i++) {
    if (rob[i] == -1)
      cands[minp[i]].push_back(i);
    else
      cands[rob[i]].push_back(i);
  }
  vector<pair<int, int> > ret;
  for (int i = 2; i <= N; i++) {
    for (int j = 0; j < (int)cands[i].size() - 1; j += 2)
      ret.push_back(make_pair(cands[i][j], cands[i][j + 1]));
  }
  printf("%d\n", ret.size());
  for (int i = 0; i < ret.size(); i++)
    printf("%d %d\n", ret[i].first, ret[i].second);
  return 0;
}
