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 codechef; // don't place package name! */
  
  import java.io.*;
  import java.util.*;
  public final class PROBOBAL {
      
      
  	public static void main(String[] args)throws IOException {
  	    
  		
  		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
  		int t=Integer.parseInt(br.readLine()),n=0,j=0,l=0,c=0,c1=0;
  		double d=0;
  		
  		for(int i=1;i<=t;i++)
  		{
  		    boolean b=true;
  		    c=0;
  		    n=Integer.parseInt(br.readLine());
  			String arg[]=br.readLine().split(" ");
  		    int a[]=new int[n];
  		    Set<Integer> h = new HashSet<Integer>();
  		    for(j=0;j<n;j++)
  		    {
  		        a[j]=Integer.parseInt(arg[j]);
  		        if(a[j]>n)
  		        c++;
  		        else
  		        h.add(a[j]);
  		    }  
  		    
  		    Arrays.sort(a);
  		    List<Integer> ht=new ArrayList<>();
  		    if(a[0]>n)
  		    ht.add(a[0]);
  		    for(j=1;j<n;j++)
  		    {
  		        if(a[j]==a[j-1]||a[j]>n)
  		        ht.add(a[j]);
  		        
  		    }
  		   
  		    c1=n-c;
  		    c=0;
  		    b=true;
  		    for(j=1;j<=n&&b;j++)
  		    {
  		        if(!h.contains(j))
  		        {
  		            l=ht.get(0);
  		            if(l>2*j)
  		            c++;
  		            else
  		            b=false;
  		            ht.remove(0);
  		        }
  		    }
  		    if(b)
  		    System.out.println(c);
  		    else
  		    System.out.println(-1);
  		}
  		
  	}
  }