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 com.company;
  
  import java.util.*;
  import java.lang.*;
  import java.io.*;
  
  public class Buffered_Reader {
      public static void main(String[] args) throws IOException {
          BufferedReader sc = new BufferedReader(new InputStreamReader(System.in));
          PrintWriter out = new PrintWriter(System.out);
  
          int t = Integer.parseInt(sc.readLine());
          while (t-->0) {
              int n = Integer.parseInt(sc.readLine());
              String[] s = sc.readLine().split(" ");
              boolean[] arr = new boolean[n+1];
              int [] x = new int[n];
              for (int i = 0; i < n; i++) x[i] = Integer.parseInt(s[i]);
  
              ArrayList<Integer> a = new ArrayList<>();
              for (int i = 0; i < n; i++) {
                  if (x[i] <= n && !arr[x[i]]) arr[x[i]] = true;
                  else a.add(x[i]);
              }
              Collections.sort(a);
  
              int j = 0;
              boolean flag = true;
              for (int i = 1; i <= n; i++) {
                  if (!arr[i]) {
                      if (i > (a.get(j)-1)/2) {
                          flag = false;
                          break;
                      }
                      j++;
                  }
              }
  
              out.println((flag)?a.size():-1);
          }
          sc.close();
          out.close();
      }
  }
  