#include <bits/stdc++.h>
using namespace std;
vector<int> v;
vector<int> primes;
bool flag[100005];
bool flag2[100005];
void sieve(int n) {
  for (int i = 2; i <= n; i++) {
    if (!flag2[i]) {
      primes.push_back(i);
      for (int j = 2 * i; j <= n; j += i) {
        flag2[j] = true;
      }
    }
  }
  int sz = 0;
  for (int i = 1; i < primes.size(); i++) {
    v.push_back(primes[i]);
    sz++;
    for (int j = primes[i] * 3; j <= n; j += primes[i]) {
      if (!flag[j]) {
        v.push_back(j);
        sz++;
        flag[j] = true;
      }
    }
    if (sz % 2 == 1) {
      if (primes[i] * 2 <= n && !flag[primes[i] * 2]) {
        v.push_back(primes[i] * 2);
        sz++;
        flag[primes[i] * 2] = true;
      } else {
        flag[v[sz - 1]] = false;
        v.erase(v.begin() + sz - 1);
        sz--;
      }
    }
  }
  for (int i = 0; i < 1; i++) {
    for (int j = primes[i]; j <= n; j += primes[i]) {
      if (!flag[j]) {
        v.push_back(j);
        sz++;
        flag[j] = true;
      }
    }
    if (sz % 2 == 1) {
      flag[v[sz - 1]] = false;
      v.erase(v.begin() + sz - 1);
      sz--;
    }
  }
}
int main() {
  int n;
  scanf("%d", &n);
  if (n < 4) {
    printf("0\n");
    return 0;
  }
  sieve(n);
  printf("%d\n", v.size() / 2);
  for (int i = 0; i < v.size(); i++) {
    printf("%d%s", v[i], (i & 1) ? "\n" : " ");
  }
  return 0;
}
