#include <bits/stdc++.h>
using namespace std;
int cnt[5];
int main() {
  int n, t;
  cin >> n;
  memset(cnt, 0, sizeof(0));
  for (int i = 0; i < n; i++) {
    cin >> t;
    cnt[t]++;
  }
  bool flag = true;
  int ret = 0;
  int minN = min(cnt[1], cnt[2]);
  cnt[3] += minN;
  cnt[1] -= minN;
  cnt[2] -= minN;
  ret += minN;
  if (cnt[1] != 0) {
    while (cnt[1] >= 3) {
      cnt[3]++;
      ret += 2;
      cnt[1] -= 3;
    }
    if (cnt[1] == 1) {
      if (cnt[3] > 0) {
        cnt[4] + 1;
        cnt[3]--;
        cnt[1] = 0;
        ret += 1;
      } else if (cnt[4] >= 2) {
        cnt[4] -= 2;
        cnt[3] += 3;
        cnt[1] = 0;
        ret += 2;
      } else
        flag = false;
    } else if (cnt[1] == 2) {
      if (cnt[4] > 0) {
        cnt[4] -= 1;
        cnt[3] += 2;
        ret += 2;
        cnt[1] = 0;
      } else if (cnt[3] >= 2) {
        cnt[3] -= 2;
        cnt[4] += 2;
        cnt[1] = 0;
        ret += 2;
      } else
        flag = false;
    }
  } else {
    while (cnt[2] >= 3) {
      cnt[2] -= 3;
      ret += 2;
      cnt[3] += 2;
    }
    if (cnt[2] == 1) {
      if (cnt[4] > 0) {
        cnt[4]--;
        cnt[3] += 1;
        cnt[2] = 0;
        ret++;
      } else if (cnt[3] > 1) {
        cnt[4] += 2;
        cnt[3] -= 2;
        cnt[2] = 0;
        ret += 2;
      } else
        flag = false;
    } else if (cnt[2] == 2) {
      cnt[2] = 0;
      cnt[4]++;
      ret += 2;
    }
  }
  if (flag)
    cout << ret << endl;
  else
    cout << -1 << endl;
  return 0;
}
