#include <bits/stdc++.h>
using namespace std;
#define RN return
#define forw(_,l,r) for(auto _=(l);_<(r);++_)
#define fors(_,r,l) for(auto _=(r);_>(l);--_)
#define fastio cin.tie(0),cout.tie(0),ios::sync_with_stdio(0);
typedef long long ll;
#define int ll
const int NUM=5e5+10;
int ls1[NUM],ls2[NUM],*a,*b;
int m,n1,n2;
void clear(){
    n1=n2=0;
    a=ls1,b=ls2;
}
ll calc(){
    int pt1=m-1,pt2=0,pt3=1;
    bool carry=0;
    while(pt1>=0&&a[pt1]==0)--pt1;
    if(pt1==-1)RN 0;
    while(pt3<m&&(b[pt3]==0||pt1+pt3<m))++pt3;
    if(pt3==m)RN 0;
    --a[pt1],--b[pt3],carry=1;
    ll ans=1;
    while(pt1>=0){
        if(a[pt1]==0){
            --pt1;continue;
        }
        while(pt2<m&&(b[pt2]==0||pt2+pt1<m-1))++pt2;
        if(pt2==m){
            carry==0;
            break;
        }
        int mi=min(a[pt1],b[pt2]);
        // cout<<"---"<<mi<<'\n';
        ans+=mi,a[pt1]-=mi,b[pt2]-=mi;
        if(a[pt1]==0)--pt1;
        if(b[pt2]==0)++pt2;
    }
    if(carry){
        ans+=b[m-1];
    }
    RN ans;
}
void test(){

}
signed main()
{
    fastio;
    int t; cin>>t;
    forw(_,0,t){
        cin>>m;
        clear();
        forw(i,0,m){
            cin>>ls1[i];
            n1+=ls1[i];
        }
        forw(i,0,m){
            cin>>ls2[i];
            n2+=ls2[i];
        }
        if(n1>n2){
            swap(a,b),swap(n1,n2);
        }
        cout<<calc()<<'\n';
    }
    RN 0;
}

/*
5
2
3 4
1 2
3
1 0 1
0 1 0
4
1 1 1 1
1 0 0 1
5
123456 114514 1919810 233333 234567
20050815 998244353 0 0 0
10
5 3 5 3 2 4 2 4 1 5
9 9 8 2 4 4 3 5 3 0

1
2
1 2
3 4
*/