#include<bits/stdc++.h>
#define ll long long
using namespace std;
ll check(ll n){
ll y=2;
ll z=n-1;
while(1){
y=y*2;
if((z%y)==0)
return y/2;
z=n-y+1;
}
}
int main(){
int t;
cin>>t;
while(t--){
int k;
cin>>k;
ll n[k];
ll m=1e18;
ll p=0,even=0;
vector <ll> odd;
for(int i=0;i<k;i++){
cin>>n[i];
if(n[i]%2==0){
even++;
}else{
odd.push_back(n[i]);
}
}
if(k%2==0){
cout<<0<<endl;
continue;
}
else{
if(even>0){
cout<<"1"<<endl;
}
else{
for(int i=0;i<odd.size();i++){
ll val=check(odd[i]);
if(val<=odd[i]) m=min(m,val);
}
if(m==1e18){
cout<<"-1\n";
}else{
cout<<m<<endl;
}
}
}
}
}
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