#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  cout << n / 2 << "\n";
  if (n % 2) {
    for (int i = 0; i < n / 2 - 1; i++) cout << 2 << " ";
    cout << 3;
  } else {
    for (int i = 0; i < n / 2; i++) cout << 2 << " ";
  }
  return 0;
}
