static int findMissingNumber(int start, int end, List<Integer> list) {
		boolean[] isMissing = new boolean[end - start + 1];
		Arrays.fill(isMissing, false);
		for (var item : list) {
			isMissing[item - start] = true;
		}
		for (int i = 0; i < isMissing.length; i++) {
			if (!isMissing[i])
				return i + start;
		}
		return -1;
}