B_AND_Sorting.cpp

#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
using namespace std;

#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL);
#define endl '\n'
#define all(x) (x).begin(), (x).end()
#define rep(i, a, b) for (int i = a; i < b; i++)

void solve() {

}

int main() {
    fastio;

    int t;
    cin >> t;
    for(int k = 1;k<=t;k++){
        int n;
        cin>>n;

        vector<int> arr(n);
        for(int i=0;i<n;i++){
            cin>>arr[i];
        }

       int ans = 1;
          for(int i=0;i<30;i++){
            ans = ans<<1;
            //cout<<ans<<" ";
            ans+=1;
        }
        for(int i=0;i<n;i++){
            if(arr[i]!=i) ans&=arr[i];
        }

        cout<<ans<<endl;

    }

    return 0;
}