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.io.*;
  import java.util.*;
  import java.util.Map.Entry;
  
  public class Div21608B {
  
  	public static void main(String[] args) throws IOException {
  
  		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
  		PrintWriter pw = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
  		
  		int t = Integer.parseInt(br.readLine());		
  	
  	    while(t --> 0){
  	        
  	        int n = Integer.parseInt(br.readLine());	
  	        
  	        ArrayList<Integer> ar = new ArrayList<Integer>();
  	        StringTokenizer st = new StringTokenizer(br.readLine());
  	        
  	        boolean[] cont = new boolean[n+1];
  	        
  	        for(int i = 0; i < n; i++){
  	            
  	            int v = Integer.parseInt(st.nextToken());
  	            
  	            if(v > n || cont[v])
  	                ar.add(v);
  	            else if(v <= n)
  	                cont[v] = true;
  	            
  	        }
  	        
  	        Collections.sort(ar);
  	        
  	        int score = 0;
  	        int ind = 0;
  	        
  	        boolean g = true;
  	        
  	        for(int i = 1; i <= n; i++){
  	             
  	            if(cont[i])
  	                continue;
  	             
  	            if(ar.get(ind) >= 2*i+1){
  	                
  	                score++;
  	                ind++;
  	                
  	            }else
  	                g = false;
              
  	        }
  	        
  	        if(g)
  	            pw.println(score);
  	        else
  	            pw.println(-1);
  	            
  	    }
  	    
  	    pw.close();
  
  	}
  
  }