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 Codeforces {
  
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        PrintWriter writer = new PrintWriter(System.out);
        int T = Integer.parseInt(br.readLine());
        while(T-- > 0) {
          int n = Integer.parseInt(br.readLine());
          Integer[] a = new Integer[n];
          StringTokenizer st = new StringTokenizer(br.readLine());
          for(int i = 0; i < n; i++) a[i] = Integer.parseInt(st.nextToken());
          Arrays.sort(a);
          boolean ans = true;
          boolean[] check = new boolean[n+1];
          int iter = 1;
          int count = 0;
          for(int i = 0; i < n && ans; i++) {
            int x = a[i];
            int q = a[i]/2;
            if(a[i]%2 != 0) q++;
            if(x < n+1) {
              if(!check[x]) {
                check[x] = true;
                continue;
              }
            }
            for(; iter < n+1; iter++) {
              if(!check[iter]) break;
            }
            if(iter < q) {
              count++;
              check[iter] = true;
            }
            else ans = false;
          }
          if(ans) writer.println(count);
          else writer.println(-1);
        }
        writer.close();
        br.close();
    }
  
  }
  