public long specialPalindrome(long n) {
 if (!inited) {
 synchronized (Solution.class) {
 if (!inited) {
 initPool();
 inited = true;
 }
 }
 }
 int idx = Collections.binarySearch(pool, n);
 if (idx < 0) {
 idx = -idx - 1;
 } else {
 idx++; 
 }
 return pool.get(idx);
}
private void initPool() {
 Consumer<String> addIfOk = s -> {
 if (s.isEmpty() || s.length() >= 17) {
 return;
 }
 try {
 long value = Long.parseLong(s);
 pool.add(value);
 } catch (NumberFormatException e) {
 }
 };
 BiConsumer<int[], Consumer<String>> gen = (cnt, adder) -> {
 int totalLength = 0;
 for (int d = 1; d <= 9; d++) {
 totalLength += cnt[d];
 }
 if (totalLength == 0 || totalLength > 17) {
 return;
 }
 int[] halfCnt = new int[10];
 for (int d = 1; d <= 9; d++) {
 halfCnt[d] = cnt[d] / 2;
 }
 final int halfLength;
 {
 int temp = 0;
 for (int d = 1; d <= 9; d++) {
 temp += halfCnt[d];
 }
 halfLength = temp;
 }
 final char mid;
 {
 char tempMid = 0;
 for (int d = 1; d <= 9; d++) {
 if ((cnt[d] & 1) == 1) {
 tempMid = (char) ('0' + d);
 break;
 }
 }
 mid = tempMid;
 }
 StringBuilder half = new StringBuilder();
 int[] hc = halfCnt.clone(); 
 Runnable dfs = new Runnable() {
 @Override
 public void run() {
 if (half.length() == halfLength) {
 String reversed = new StringBuilder(half).reverse().toString();
 String palindrome;
 if (mid != 0) {
 palindrome = half.toString() + mid + reversed;
 } else {
 palindrome = half.toString() + reversed;
 }
 adder.accept(palindrome);
 return;
 }
 for (int d = 1; d <= 9; d++) {
 if (hc[d] == 0) {
 continue;
 }
 hc[d]--;
 half.append((char) ('0' + d));
 this.run(); 
 half.deleteCharAt(half.length() - 1); 
 hc[d]++;
 }
 }
 };
 dfs.run();
 };
 int[] evenDigits = {2, 4, 6, 8};
 int[] oddDigits = {1, 3, 5, 7, 9};
 for (int mask = 1; mask < (1 << 4); mask++) {
 int[] cnt = new int[10];
 int totalLength = 0;
 for (int i = 0; i < 4; i++) {
 if ((mask & (1 << i)) != 0) {
 int d = evenDigits[i];
 cnt[d] = d;
 totalLength += d;
 }
 }
 if (totalLength <= 17) {
 gen.accept(cnt, addIfOk);
 }
 }
 for (int odd : oddDigits) {
 for (int mask = 0; mask < (1 << 4); mask++) {
 int[] cnt = new int[10];
 int totalLength = odd;
 cnt[odd] = odd;
 for (int i = 0; i < 4; i++) {
 if ((mask & (1 << i)) != 0) {
 int d = evenDigits[i];
 cnt[d] = d;
 totalLength += d;
 }
 }
 if (totalLength <= 17) {
 gen.accept(cnt, addIfOk);
 }
 }
 }
 Collections.sort(pool);
 List<Long> uniquePool = new ArrayList<>(new LinkedHashSet<>(pool));
 pool.clear();
 pool.addAll(uniquePool);
}