Suppose you are car driver and you have to drive a car on a track divided into "N" no. of sub-tracks. You are also given the value of "K" i.e. the total kilometers a car can drive on each sub-track. If the car can't cover a sub-track, you can add any unit of Petrol in it. With each unit of petrol added, the total kilometers your car can travel will increase by one unit .

**Input:**

The first line of input contains an integer T denoting the no of test cases. Then T test cases follow. Each test case contains two space separated integers N and K. The second line of each test case contains N space separated integers (A[]) denoting the distance of each N sub-tracks.

**Output:**

For each test case in a new line you have to print out the minimum unit of Petrol your car require to cover all the sub-tracks. If no extra unit of petrol is required, print -1.

**Constraints:**

1<=T<=100

1<=N,K<=200

1<=A[]<=1000

**Example:**

Input:

2

5 7

2 5 4 5 2

5 4

1 6 3 5 2

**Output:**

-1

2

**Explanation:**

In Case 2, you are given 5 sub-tracks with different kilometers. Your car can travel 4 km on each sub-track. So, when you come on sub-track 2nd you have to cover 6 km of distance, so you need to have 2 unit of petrol more to cover the distance, for 3rd sub-track, now your car can travel 6 kilometers, so no problem and so on.

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