Milly is playing with an Array A of size N. She wants to convert this array into a magical array. This magical array satisfies the condition A_i-1 < A_i where i ∈ [2, N] . She can add a value X to any element of this array any number of times. Your task is to tell her the minimum number of such addition of X are required in order to get the magical array.

Input

• First line of the input will contain T(No. of test cases).
• For every test case, first line will contain two space separated integers denoting N and X. Next line will contain N space separated integers denoting A_i.

Output

• For every test case, print the required answer in a new line.

Constraints

• 1 ≤ T ≤ 10
• 2 ≤ N ≤ 10⁵
• 1 ≤ X ≤ 10⁹
• 1 ≤ A_i ≤ 10⁹