class Solution {
	public int smallestRepunitDivByK(int K) {
		HashSet<Integer> set = new HashSet<>();
		int sum = 0;
		for (int i = 1; i <= 1000000; ++i) {
			sum = (sum * 10 + 1) % K;
			if (sum == 0)
				return i;
			if (set.contains(sum))
				return -1;
			set.add(sum);
		}
		return -1;
	}
}