#include <bits/stdc++.h>   #pragma GCC optimize( O2 )   using namespace std;   void solve() {     int n;     cin >> n;     set<int> s;     for (int i = 0; i < n; i++) {       int a;       cin >> a;       s.insert(a);     }     for (int cnt = 1; cnt <= 1023; cnt++) {       bool vis[1025];       memset(vis, 0, sizeof(vis));       bool h = 1;       for (auto x : s) {         if (vis[x ^ cnt] || s.count(x ^ cnt) == 0) {           h = 0;           break;         }         vis[x ^ cnt] = 1;       }       if (h) {         cout << cnt;         return;       }     }     cout << -1;   }   int main() {     ios::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     int t;     cin >> t;     while (t--) {       solve();       cout <<   n ;     }   }   