#include <bits/stdc++.h>
    #include <chrono>
    using namespace std;
    using namespace chrono;
    // "AJEET JAIN"----"JAI JINENDRA"  
    /* "णमो अरिहंताणं",
        "णमो सिद्धाणं",
        "णमो आयरियाणं",
        "णमो उवज्झायाणं",
        "णमो लोए सव्वसाहूणं",
        "",
        "एसो पंच नमोक्कारो, सव्व पावप्पणासणो",
        "मंगलाणं च सव्वेसिं, पडमं हवै मंगलं",   */
 
 
    // Aliases to op
    using ll = long long;
    using ull = unsigned long long;
    using ld = double;
    using vll = vector<ll>;
 
 
    // Constants
    constexpr ll INF = 4e18;
    constexpr ld EPS = 1e-9;
    constexpr ll MOD = 1e9 + 7;
 
 
 
    // Macros
    #define F first
    #define S second
    #define all(x) begin(x), end(x)
    #define allr(x) rbegin(x), rend(x)
    #define py cout<<"YES\n";
    #define pn cout<<"NO\n";
    #define forn(i,n) for(int i=0;i<n;i++)
    #define for1(i,n) for(int i=1;i<=n;i++)
 
    // #define insert push_back
    #define pb push_back
    #define MP make_pair
    #define endl '\n'
 
 
 
     /*
      
     Golden Rule
 
     1) problem is easy
     2) proofs is easy
     3) implementation is easy
     
     /*
         ROUGH --
                 
     */
 
    void AJNJ(){
       ll n;
       cin >> n;
       vector<ll> v(n);
       map<ll , ll> mp;
       forn(i , n){
          cin >> v[i];
          mp[v[i]]++;
       }
 
       for(auto x : mp){
          if(x.S == 1){
             cout << "-1" << endl;
             return;
          }
       }
       ll ans = 0;
 
       for(auto x : mp){
          if((x.S) % 3 == 0){
             ans += (x.S)/3;
          }
          else if(((x.S) % 3)%2 == 0){
             ans += (x.S)/3 + 1;
          }
          else{
             ans += (x.S)/2;
          }
       }
 
       cout << ans << endl;
 
 
    }
 
 
    int main(){
        ios::sync_with_stdio(0);
        cin.tie(0);
        cout.tie(0);
        int T = 1;
        cin>>T;
        auto start1 = high_resolution_clock::now();
        while(T--){
            AJNJ();
        }
        auto stop1 = high_resolution_clock::now();
        auto duration = duration_cast<microseconds>(stop1 - start1);
        cerr << "Time: " << duration . count() / 1000 << " ms" << endl;
 
        return 0;
    }

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