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 java.util.*;
  import java.io.*;
  public class C_Paprika_and_Permutation{
      public static void solve(int a[],int n){
          TreeSet<Integer> set=new TreeSet<>();
          for(int i=1;i<=n;i++){
              set.add(i);
          }
          for(int i=0;i<n;i++){
              if(set.contains(a[i])){
                  set.remove(a[i]);
                  a[i]=-1;
              }
          }
         // System.out.println(set);
          Arrays.sort(a);
          int ans=0;
          for(int i=0;i<n;i++){
              if(a[i]!=-1){
                   if(set.floor((a[i]-1)/2)!=null){
                       ans++;
                       set.remove(set.floor((a[i]-1)/2));
                   }else {
                       System.out.println(-1);return;
                   }
              }
          }
          System.out.println(ans);
          
      }
      public static void main(String args[]){
          Scanner sc=new Scanner(System.in);
          int t=sc.nextInt();
          while(t-->0){
              int n=sc.nextInt();
              int a[]=new int[n];
              for(int i=0;i<n;i++){
                  a[i]=sc.nextInt();
              }
              solve(a,n);
          }
      }
  }