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: #include <bits/stdc++.h>
  #pragma GCC diagnostic ignored "-Wunused-variable"
  #pragma GCC diagnostic ignored "-Wunused-parameter"
  using namespace std;
  #pragma GCC diagnostic ignored "-Wunused-but-set-variable"
  #pragma GCC diagnostic ignored "-Wformat"
  mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
  long long power(long long B, long long P) {
    if (P == 0) return 1;
    long long X = power(B, P / 2);
    if (P % 2 == 0)
      return X * X;
    else
      return B * X * X;
  }
  int fx[] = {1, -1, 0, 0};
  int fy[] = {0, 0, 1, -1};
  int main() {
    int T, cs = 0;
    scanf("%d", &T);
    while (T--) {
      int n;
      scanf("%d", &n);
      set<int> st;
      vector<int> v;
      for (int i = 1; i <= n; i++) st.insert(i);
      for (int i = 1; i <= n; i++) {
        int u;
        scanf("%d", &u);
        if (st.find(u) != st.end())
          st.erase(u);
        else
          v.push_back(u);
      }
      sort(v.rbegin(), v.rend());
      int res = 0;
      for (auto it : v) {
        auto ck = st.end();
        ck--;
        if (*ck > (it - 1) / 2) {
          res = 1;
          break;
        }
        st.erase(ck);
      }
      if (res == 1)
        cout << "-1\n";
      else
        cout << v.size() << endl;
    }
    return 0;
  }
  