#include <bits/stdc++.h>
#define int long long
using namespace std;
 
void solve() {
    int n;
    cin >> n;
   vector<int> v(n);
   for(int i=0;i<n;i++){
   		cin>>v[i];
   }
   int x=-1;
   for(int i=0;i<n;i++){
   		if(v[i]!=i){
   			int y=(v[i]&v[v[i]]);
   			if(x==-1)x=y;
   			else{
   				x=(x & y);
   			}
   		}
   }
   cout<<x<<endl;
 
 
}
 
signed main() {
    int t;
    cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}
 

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4
4
0 1 3 2
2
1 0
7
0 1 2 3 5 6 4
5
0 3 2 1 4