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: //Paprika and Permutation
  import java.io.*;
  import java.util.*;
  
  public class C1617{
     
     public static void main(String[] args)throws IOException{
        BufferedReader f = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter out = new PrintWriter(System.out);
        
        int t = Integer.parseInt(f.readLine());
        
        for(int q = 1; q <= t; q++){
  
           int n = Integer.parseInt(f.readLine());
        
           StringTokenizer st = new StringTokenizer(f.readLine());
           Integer[] array = new Integer[n];
           
           HashSet<Integer> hset = new HashSet<Integer>();
           ArrayList<Integer> notused = new ArrayList<Integer>();
           for(int k = 0; k < n; k++){
              array[k] = Integer.parseInt(st.nextToken());
              
              if(array[k] > n || hset.contains(array[k])){
                 notused.add(array[k]);
              } else {
                 hset.add(array[k]);
              }
           }
        
           Collections.sort(notused);
           int nui = 0;
           
           boolean fail = false;
           int answer = 0;
           for(int k = 1; k <= n; k++){
              if(hset.contains(k)) continue;
              
              if((notused.get(nui)-1)/2<k){
                 fail = true;
                 break;
              } else {
                 answer++;
              }
              
              nui++;
           }
           
           if(fail){
              out.println(-1);
           } else {
              out.println(answer);
           }
        }
        
        
        
        
        out.close();
     }
     
        
  }