#include <bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
//using namespace __gnu_pbds;
using namespace std;
/* #pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")*/
typedef long long ll;
const ll MAXK = 3e3 + 5;
const ll MOD = 1e9 + 7;
const ll MODH = 1e9 + 9;
const int MAXLG = 20;
const long double PI = acos(-1);
const ll p = 41;
const long double EPS = 1e-4;
#define x first
#define y second
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
inline ll rand(ll a, ll b) {ll c = rng(); return a+((ll)abs(c))%(b-a+1);}
ll binpowmod(ll a, ll b, ll m) {a %= m;ll res = 1;while (b > 0) {if (b & 1){res = res * a % m;}a = a * a % m;b >>= 1;
 
}return res;}
//typedef tree<ll, null_type, less_equal<ll>, rb_tree_tag,  //less_equal
  //           tree_order_statistics_node_update> oset;
const int MAXN = 1e6 + 5;


int main()
{

ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);


int t;
cin >> t;
while(t--)
{
  int n;
  cin >> n;
  multiset<int,greater<int>> se;
  for(int i = 0 ; i < n ; i++)
     {
      int x;
      cin >> x;
      se.insert(x);
     }

  int top = *se.begin();
  if(se.count(top) > 2)
  {
    cout << -1 << '\n';
    continue;
  }
  cout << (int)se.size() - (se.count(top) - 1) << '\n';




}




 
}