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: import sys,os,io
  input = io.BytesIO(os.read(0, os.fstat(0).st_size)).readline
  #input = sys.stdin.readline
  import math
  import bisect
  t=int(input())
  for a0 in range(t):
      n=int(input())
      l=[int(i) for i in input().split()]
      l.sort()
      f=0 
      c=0
      perm=[0]*n 
      ind=0 
      l1=[]
      for i in range(n):
          if(l[i]<=n):
              perm[l[i]-1]+=1 
              if(perm[l[i]-1])>1:l1.append(l[i])
          else:
              ind=i 
              break 
      l1.extend(l[ind::])
      #print(l1)
      i=0 
      ind=0 
      #print(perm,ind)
      while(ind<n and i<n):
          if(perm[i]==0):
              if(l1[ind]%2!=0):
                  l1[ind]+=1 
              if(l1[ind]//2<=i+1):
                  #print(l1[ind],i+1)
                  f=1 
                  break 
              else:
                  c+=1
                  ind+=1 
          i+=1 
      if(f==1):
          #print(ind,i)
          print(-1)
      else:
          print(c)