description: Paprika loves permutations. She has an array a_1, a_2, ..., a_n. She wants to make the array a permutation of integers 1 to n.
  
  In order to achieve this goal, she can perform operations on the array. In each operation she can choose two integers i (1 ≤ i ≤ n) and x (x > 0), then perform a_i := a_i mod x (that is, replace a_i by the remainder of a_i divided by x). In different operations, the chosen i and x can be different.
  
  Determine the minimum number of operations needed to make the array a permutation of integers 1 to n. If it is impossible, output -1.
  
  A permutation is an array consisting of n distinct integers from 1 to n in arbitrary order. For example, [2,3,1,5,4] is a permutation, but [1,2,2] is not a permutation (2 appears twice in the array) and [1,3,4] is also not a permutation (n=3 but there is 4 in the array).
  
  Input
  
  Each test contains multiple test cases. The first line contains a single integer t (1 ≤ t ≤ 10^4) — the number of test cases. Description of the test cases follows.
  
  The first line of each test case contains an integer n (1 ≤ n ≤ 10^5).
  
  The second line of each test case contains n integers a_1, a_2, ..., a_n. (1 ≤ a_i ≤ 10^9).
  
  It is guaranteed that the sum of n over all test cases does not exceed 2 ⋅ 10^5.
  
  Output
  
  For each test case, output the minimum number of operations needed to make the array a permutation of integers 1 to n, or -1 if it is impossible.
  
  Example
  
  Input
  
  
  4
  2
  1 7
  3
  1 5 4
  4
  12345678 87654321 20211218 23571113
  9
  1 2 3 4 18 19 5 6 7
  
  
  Output
  
  
  1
  -1
  4
  2
  
  Note
  
  For the first test, the only possible sequence of operations which minimizes the number of operations is: 
  
    * Choose i=2, x=5. Perform a_2 := a_2 mod 5 = 2. 
  
  
  
  For the second test, it is impossible to obtain a permutation of integers from 1 to n.
solution: # your code goes here
  # your code goes here
  import sys
  import math
  from fractions import Fraction
  from decimal import *
  input = sys.stdin.readline
  
  
  t = int(input())
  while t>0:
  	n = int(input().strip())
  	inp = input().strip()
  	arr = [int(x) for x in inp.split(' ')]
  
  	present = [0]*(n+1)
  
  	arr.sort()
  
  	ans = 0
  	cur = 1
  
  	for a in arr:
  		if a<=n:
  			if present[a] == 0:
  				present[a] = 1
  			else:
  				while cur<=n and present[cur]==1:
  					cur+=1
  				if a>=2*cur+1:
  					ans += 1
  					cur += 1
  				else:
  					ans = -1
  					break
  		else:
  			while cur<=n and present[cur]==1:
  				cur+=1
  			if a>=2*cur+1:
  				ans += 1
  				cur += 1
  			else:
  				ans = -1
  				break
  
  	print(ans)
  
  
  	t -= 1
  
  