#include <bits/stdc++.h>
#include <set>
using namespace std;

int main() {
    int q; cin>>q;
    while(q--) {
        int n ; cin>>n;
        set<int,greater<>> s;
        int y;
        while(n--) {
            cin>>y;
            s.insert(y);
        }
        if(s.size()<=1) cout<<-1<<endl;
        else {
            auto it = s.begin();
            it++;
            cout<<*it<<endl;
        }
    }

}