#include<bits/stdc++.h>
using namespace std;
 
int n;
vector<int> a;
 
int solve(int l,int r){
    set<int> s;
    for(int i=0;i<=n;i++) s.insert(i);
 
    while(l>=0&&r<2*n&&a[l]==a[r]){
        s.erase(a[l]);
        l--;
        r++;
    }
 
    return *s.begin();
}
 
int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
 
    int t;
    cin>>t;
 
    while(t--){
        cin>>n;
        a.assign(2*n,0);
 
        for(int i=0;i<2*n;i++) cin>>a[i];
 
        int x=-1,y=-1;
 
        for(int i=0;i<2*n;i++){
            if(a[i]==0){
                if(x==-1) x=i;
                else y=i;
            }
        }
 
        cout<<max({solve(x,x),solve(y,y),solve((x+y)/2,(x+y+1)/2)})<<"\n";
    }
 
    return 0;
}

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6
4
1 2 0 3 3 0 2 1
2
0 1 0 1
2
1 1 0 0
3
2 0 2 1 1 0
4
0 1 3 0 3 1 2 2
3
0 1 2 1 0 2