#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--){
    int n;
    cin>>n;
    int a[n];
    for(int i=0;i<n;i++){cin>>a[i];}
    if(n%2==1){
        int x=a[0];
        for(int i=0;i<n;i++)x=((x|a[i]));
        cout<<x<<"\n";
    }
    else {
        int x=a[0];
        for(int i=0;i<n-1;i++)x=((x|a[i]));
        if((x&a[n-1])==a[n-1])cout<<-1<<"\n";
        else cout<<x<<"\n";
    }
   }
    return 0;
}
