/*                        I am not the best, but I am better than your father.                                          */
#include <bits/stdc++.h>
using namespace std;
using ll=long long ;
#define len(s) (int)s.size()
#define ss second
#define ff first
#define all(a) a.begin(),a.end()
#define s(a,b) for ( int i = a ; i < b ; i++)
#define q(a,b) for ( int j = a ; j < b ; j++)
void solve ()
{
 int n , m ;
 cin >>n >> m;
 ll arr[20];
 arr[0]=1;
 s(1,20)
 arr[i]=i*arr[i-1];

 cout<< arr[n]/(arr[m]*arr[n-m])<<endl;
/*s(0,20)
cout<<arr[i]<<endl;*/
}
void solve2()
{
    int n;
     cin>>n;
     int arr[n], arr1[n];
     s(0,n)
     cin>>arr[i];
     s(0,n)
     cin>>arr1[i];
     int ma= 0;
     s(0,n)
     {
         if(arr1[i]>arr[i])
         {
         int z =arr1[i]-arr[i];
         ma=max(ma,z);
     }}
     cout<<ma<<"\n";
}
void solve3()
{
    string str ;
    bool p = true;
    cin >>str ;
    int c = len (str)/2;
    if(len(str)%2==1)
        c++;
    s(0,c)
    {
        if(str[i]!=str[i+c] && p)
        {
            cout<<"No\n";
            p=false;
    }}
    if(p)
    cout<<"Yes\n";

}
void solve4 ()
{
    int n;
     cin>> n;
      int arr[n];
      int counter = 0;
      s(0,n)
      {
          cin>>arr[i];
          if(arr[i]==8)
              counter++;
      }
      if(counter ==2)
          cout<<n/2+1<<endl;
      else if(counter > 2)
          cout<<-1<<endl;
      else
          cout<<n;
}
int main() {
  // solve();
  ll t;
  cin >> t;
  while(t--){
     solve4();
}}