#include<iostream>
#include<cstdio>
using namespace std;
int ans,t,n;
int main()
{
    freopen("and_sorting.in","r",stdin);
    freopen("and_sorting.out","w",stdout);
    int k;
    bool f;
    scanf("%d",&t);
    while(t--)
    {
        ans=f=0;
        scanf("%d",&n);
        for(int i=0;i<n;++i)
        {
            scanf("%d",&k);
            if(k!=i)
            {
                if(!f) ans=i,f=1;
                ans&=i;
            }
        }
        printf("%d\n",ans);
    }
    return 0;
}