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.*;
  
  public class Main {
  	
  	
  	public static void main(String[] args) throws Exception {
  		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
  		BufferedWriter out = new BufferedWriter(new OutputStreamWriter(System.out));		
  		
  		int num_tests = Integer.parseInt(in.readLine());
  		int[] A = new int[200200];
  		int[] count = new int[200200];
  		int[] start = new int[200200];
  		int[] end = new int[200200];
  		
  		for (int ts=1; ts<=num_tests; ts++) {
  			int N = Integer.parseInt(in.readLine());
  			
  			{
  				int idx=1;
  				for (final String st : in.readLine().split(" ")) {
  					A[idx] = Integer.parseInt(st);
  					idx++;
  				}
  			}
  			
  			for (int i=1; i<=N; i++) {
  				count[i] = 0;
  				start[i] = 0;
  				end[i] = 0;
  			}
  			
  			int ans = 0;
  			
  			for (int i=1; i<=N; i++) {
  				if (A[i] <= N) {
  					if (count[A[i]] > 0) {
  						if ((A[i]-1)/2 >= 1) {
  							start[1]++;
  							end[(A[i]-1)/2]++;
  						}
  						ans++;
  					}
  					count[A[i]]++;
  				} else {
  					if ((A[i]-1)/2 >= 1) {
  						start[1]++;
  						end[Math.min((A[i]-1)/2, N)]++;
  					}
  					ans++;
  				}
  			}
  			
  			/*out.write("start: \n");
  			for (int i=1; i<=N; i++) {
  				out.write(" " + start[i]);
  			}
  			out.write("\n\n");
  			out.write("end: \n");
  			for (int i=1; i<=N; i++) {
  				out.write(" " + end[i]);
  			}
  			out.write("\n");
  
  			out.write("count: \n");
  			for (int i=1; i<=N; i++) {
  				out.write(" " + count[i]);
  			}
  			out.write("\n");*/
  			
  			
  			int unfilled = 0;
  			for (int i=1; i<=N; i++) {
  				if (count[i] == 0) unfilled++;
  			}
  			
  			int candidates = 0;
  			for (int i=1; i<=N; i++) {
  				candidates += start[i];
  				
  				if (count[i] == 0 && candidates < unfilled) {ans = -1;}
  				if (count[i] == 0) unfilled--;
  				
  				candidates -= end[i];
  			}
  			
  			
  			out.write(ans + "\n");
  			out.flush();
  			
  		}
  		
  		in.close();
  		out.close();
  	}
  
  }
  