3790. Smallest All-Ones Multiple

You are given a positive integer k. Find the smallest integer n divisible by k that consists of only the digit 1 in its decimal representation (e.g., 1, 11, 111, ...). Return an integer denoting the number of digits in the decimal representation of n. If no such n exists, return -1. Example 1: Input: k = 3 Output: 3 Explanation: n = 111 because 111 is divisible by 3, but 1 and 11 are not.