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Drive the car

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.

#### ** For More Input/Output Examples Use 'Expected Output' option **

Contributor: Mohit Gupta

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