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:   /* package codechef; // don't place package name! */
  import java.util.*;
  import java.lang.*;
  import java.io.*;
  import java.math.BigInteger;
   
   
   
   
   
  public class hello{
   
     static class Pair implements Comparable<Pair>{
   
      long val;
      long ind;
      public Pair(long val,long ind)
      {
          this.val=val;
          this.ind=ind;
      }
   
      public int compareTo(Pair o)
      {
          return Long.compare(this.val, o.val);
  }
  }
       static class FastReader 
      { 
          BufferedReader br; 
          StringTokenizer st; 
    
          public FastReader() 
          { 
              try {
                 br=new BufferedReader(new FileReader("input.txt"));
                 PrintStream out= new PrintStream(new FileOutputStream("output.txt"));
                 System.setOut(out);
              }
    
              // Catch block to handle the exceptions
              catch (Exception e) {
                  br=new BufferedReader(new InputStreamReader(System.in));
              }
          } 
    
          String next() 
          { 
              while (st == null || !st.hasMoreElements()) 
              { 
                  try
                  { 
                      st = new StringTokenizer(br.readLine()); 
                  } 
                  catch (IOException  e) 
                  { 
                      e.printStackTrace(); 
                  } 
              } 
              return st.nextToken(); 
          } 
    
          int nextInt() 
          { 
              return Integer.parseInt(next()); 
          } 
    
          long nextLong() 
          { 
              return Long.parseLong(next()); 
          } 
    
          double nextDouble() 
          { 
              return Double.parseDouble(next()); 
          } 
    
          String nextLine() 
          { 
              String str = ""; 
              try
              { 
                  str = br.readLine(); 
              } 
              catch (IOException e) 
              { 
                  e.printStackTrace(); 
              } 
              return str; 
          } 
      } 
       static int computeXOR(int n)
      {
          // If n is a multiple of 4
          if (n % 4 == 0)
              return n;
        
          // If n%4 gives remainder 1
          if (n % 4 == 1)
              return 1;
        
          // If n%4 gives remainder 2
          if (n % 4 == 2)
              return n + 1;
        
          // If n%4 gives remainder 3
          return 0;
      }
      static long helper(List<Long> l,long k)
      {
          int length = l.size()-1;
          long val = 0;
  
          while(length>=0)
          {
              val+=2*(l.get(length));
              length-=k;
          }
  
          return val;
      }
  
     static long findGCD(long a, long b){
      if(b == 0)
        return a;
      return findGCD(b, a%b);
  }
      public static void main (String[] args) throws java.lang.Exception
      {
   
         try{
          FastReader sc=new FastReader();
          BufferedWriter out = new BufferedWriter(
              new OutputStreamWriter(System.out));
          int t = sc.nextInt();
          while(t-->0)
          {
              int n = sc.nextInt();
  
              long arr[] = new long[n];
  
              HashMap<Long,Integer> map = new HashMap<>();
  
              for(int i=0;i<n;i++)
              {
                  arr[i] = sc.nextLong();
                  if(map.containsKey(arr[i]))
                  {
                      int c = map.get(arr[i]);
                      map.put(arr[i],c+1);
                  }
                  else
                  {
                      map.put(arr[i],1);
                  }
              }
  
              PriorityQueue<Long> pq = new PriorityQueue<>();
  
              for(int i=0;i<n;i++)
              {
                  long k = i+1;
                  if(map.containsKey(k))
                  {
                      int c = map.get(k);
                      if(c==1)
                          map.remove(k);
                      else
                      {
                          map.put(k,c-1);
                      }
                  }
                  else
                  {
                      pq.add(k);
                  }
              }
  
              PriorityQueue<Long> pq2 = new PriorityQueue<>();
  
              for(long key:map.keySet())
              {
                  int c = map.get(key);
                  while(c-->0)
                  {
                      pq2.add(key);
                  }
              }
  
              int count = 0;
              boolean isTrue = true;
  
              
             
             while(pq2.size()!=0&&pq.size()!=0)
             {
                  long val1 = pq2.remove();
                  long val2 = pq.remove();
  
                  long h = val1-val2;
  
                  if(val2%h==val2)
                  {
                      count++;
                  }
                  else
                  {
                      isTrue=false;
                      break;
                  }
             }
  
              if(isTrue)
              {
                  System.out.println(count);
              }
              else
              {
                  System.out.println(-1);
              }
          }
      }catch(Exception e){
              return;
          }
      }
  }