#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e6 + 5;
int ans, cnt, tmp;
int main() {
  int n;
  cin >> n;
  int a[] = {0, 0, 0, 0, 0};
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    a[x]++;
    cnt += x;
  }
  if (cnt == 5 || cnt < 3) return cout << -1, 0;
  ans += min(a[1], a[2]);
  a[1] -= ans, a[2] -= ans, a[3] += ans;
  if (a[1] != 0) {
    ans += a[1] / 3 * 2;
    a[3] += a[1] / 3;
    a[1] = a[1] % 3;
    if (a[1] == 1) {
      if (a[3] != 0)
        ans += 1;
      else
        ans += 2;
    } else if (a[1] == 2) {
      ans += 2;
    }
    return cout << ans, 0;
  } else if (a[2] != 0) {
    ans += a[2] / 3 * 2;
    a[3] += a[2] / 3 * 2;
    a[2] = a[2] % 3;
    if (a[2] == 1) {
      if (a[4] != 0)
        ans++;
      else
        ans += 2;
    } else if (a[2] == 2) {
      ans += 2;
    }
    return cout << ans, 0;
  }
  cout << ans;
  return 0;
}
