B"You are given a non-decreasing array of non-negative integers a_1, a_2, ldots, a_n . Also you are given a positive integer k . You want to find m non-decreasing arrays of non-negative integers b_1, b_2, ldots, b_m , such that: Find the minimum possible value of m , or report that there is no possible m . The first line contains one integer t ( 1 <= q t <= q 100 ): the number of test cases. The first line of each test case contains two integers n , k ( 1 <= q n <= q 100 , 1 <= q k <= q n ). The second line contains n integers a_1, a_2, ldots, a_n ( 0 <= q a_1 <= q a_2 <= q ldots <= q a_n <= q 100 , a_n > 0 ). For each test case print a single integer: the minimum possible value of m . If there is no such m , print -1 . In the first test case, there is no possible m , because all elements of all arrays should be equal to 0 . But in this case, it is impossible to get a_4 = 1 as the sum of zeros. In the second test case, we can take b_1 = [3, 3, 3] . 1 is the smallest possible value of m . In the third test case, we can take b_1 = [0, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2] and b_2 = [0, 0, 1, 1, 1, 1, 1, 2, 2, 2, 2] . It's easy to see, that a_i = b_{1, i} + b_{2, i} for all i and the number of different elements in b_1 and in b_2 is equal to 3 (so it is at most 3 ). It can be proven that 2 is the smallest possible value of m . "...