K-th missing element
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Given an increasing sequence a[], we need to find the K-th missing contiguous element in the increasing sequence which is not present in the sequence. If no k-th missing element is there output -1.

Input:
The first line consists of an integer T i.e. the number of test cases. The first line of each test case consists of two integers N and K.Next line consists of N spaced integers.

Output:
For each test case, print the Kth missing number if present otherwise print -1.

Constraints:
1<=T<=100
1<=N,K,A[i]<=105

Examples:
Input

2
5 2
1 3 4 5 7
6 2
1 2 3 4 5 6
Output
6
-1

Explanation:
#TestCase 1:

K=2
We need to find the 2nd missing number in the array. Missing numbers are 2 and 6. So 2nd missing number is 6.
#Testcase 2:
K=2
We need to find the 2nd missing number in the array. As there is no missing number, hence the output is -1.

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

Contributor: Saksham_A
Author: saksham0751

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