Append for OR

#include <bits/stdc++.h>
#define ll long long int
#define nl cout<<endl
using namespace std;

int main() {
    int t; cin>>t;
    while(t--){
        ll n,y; cin>>n>>y;
        ll arr[n];
        ll orr=0;
        for(ll i=0;i<n;i++){
            cin>>arr[i];
            orr|=arr[i];
        }
       ll ans=orr^y;
       if((ans|orr) == y) cout<<ans;
       else cout<<-1;
       nl;
    }
	// your code goes here
	return 0;
}