#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define speed ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
#define pb push_back
#define S second
#define F first
#define pii pair<int,int>
#define pll pair<ll,ll>
int main(){
    speed;
   int test;
   cin>>test;
   while(test--){
    ll n;
    cin>>n;
    ll a[n];
    map <ll,ll> mp;
    for(ll i=0;i<n;i++){cin>>a[i];
    mp[a[i]]=0;
    }
    if(n%2==1){
        ll x=a[0];
        for(ll i=0;i<n;i++)x=((x|a[i]));
        cout<<setprecision(0)<<fixed<<x<<"\n";
    }
    else {
       set <ll> st;
       for(ll i=0;i<n;i++){
            st.insert(a[i]);
       mp[a[i]]++;
    }
    ll temp=a[0];
    ll cnt=0;
    bool flag=false;
    for(ll now:st){
        temp=(temp|now);
        cnt+=mp[now];
        if(cnt%2==1){flag=true;break;}
    }
    if(flag){cout<<fixed<<setprecision(0)<<temp<<"\n";}
    else cout<<-1<<"\n";
    }
   }
    return 0;
}
