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 javax.swing.*;
      import java.io.BufferedReader;
      import java.io.IOException;
      import java.io.InputStreamReader;
      import java.io.PrintWriter;
      import java.util.*;
      public class Main extends PrintWriter {
          static BufferedReader s = new BufferedReader(new InputStreamReader(System.in));Main () { super(System.out); }public static void main(String[] args) throws IOException{ Main  d1=new Main   ();d1.main();d1.flush(); }
  
          void main() throws IOException {
              StringBuilder sb = new StringBuilder();
              int t = 1;
              t = i(s()[0]);
              while (t-- > 0) {
                 int n = i(s()[0]);
                 int[] a=new int[n];arri(a, n);
                 Arrays.sort(a);
                 int flag = 0;
                 int cnt = 0;
                 PriorityQueue<Integer> pq = new PriorityQueue<>();
                 HashMap<Integer, Integer> h = new HashMap<>();
                  HashMap<Integer, Integer> use = new HashMap<>();
                  for(int i=0;i<n;i++){
                     h.put(i + 1, 0);
                   if(a[i] == i + 1){
                       h.remove(i + 1);flag++;
                       use.put(i, 0);
                   }
                 }
                  for(int i = 0; i < n; i++) {
                      if (h.containsKey(a[i])) {
                          flag++;
                          use.put(i, 0);
                          h.remove(a[i]);
                      }
                  }int ind = 0;
                  for(int i = 0; i < n; i++){
                      if(use.containsKey(i)) continue;
                        for(int j = ind; j < n; j++){
                            if (h.containsKey(j + 1)) {
                                if(2 * (j + 1) < a[i]){
                                    flag++; cnt++;h.remove(j + 1);
                                }
                                else break;
                                ind = j + 1;
                                break;
                        }
                     }
                 }if(flag < n) sb.append("-1\n");
                 else sb.append(cnt + "\n");
              }
              System.out.println(sb);
          }  static long gcd(long a, long b) {
                  if (b == 0)
                      return a;
                  return gcd(b, a % b);
              }
          static String[] s() throws IOException { return s.readLine().trim().split("\\s+"); }
          static int i(String ss) {return Integer.parseInt(ss); }
          static long l(String ss) {return Long.parseLong(ss); }
          public void arr(long[] a,int n) throws IOException {String[] s2=s();for(int i=0;i<n;i++){ a[i]=l(s2[i]); }}
          public void arri(int[] a,int n) throws IOException {String[] s2=s();for(int i=0;i<n;i++){ a[i]=(i(s2[i])); }}
  
      }class Pair{
             int start, end;
             public Pair(long a, long b){
                 this.start = (int)a ; this.end = (int)b;
          }
      }
  
  
  