/*
Things to notice:
1. do not calculate useless values
2. do not use similar names
 
Things to check:
1. submit the correct file
2. time (it is log^2 or log)
3. memory
4. prove your naive thoughts 
5. long long
6. corner case like n=0,1,inf or n=m
7. check if there is a mistake in the ds or other tools you use
8. fileio in some oi-contest

9. module on time 
10. the number of a same divisor in a math problem
11. multi-information and queries for dp and ds problems
*/
#include<bits/stdc++.h>
using namespace std;
#define int long long
#define fi first
#define se second
#define pii pair<long long,long long>
#define mp make_pair
#define pb push_back
const int mod=998244353;
const int inf=0x3f3f3f3f;
const int INF=1e18;
int n;
int a[500005],b[500005];
void solve()
{
	cin>>n;
	int sa=0,sb=0;
	for(int i=0;i<n;i++) cin>>a[i],sa+=a[i];
	for(int i=0;i<n;i++) cin>>b[i],sb+=b[i];
	if(sa>sb) b[0]+=sa-sb;
	else a[0]+=sb-sa;
	int ans=0;
	for(int i=n-1,flg=0,j=0;i>=0;i--) if(a[i])
	{
		if(!flg)
		{
			for(int l=0;l<n;l++) if(b[l]&&l+i>=n)
			{
				ans++,b[l]--,a[i]--,flg=1;
				break;
			}
			if(!flg)
			{
				cout<<"0\n";
				return;
			}
		}
		j=max(j,n-1-i);
		while(j<n)
		{
			int d=min(a[i],b[j]);
			ans+=d;
			if(d) a[i]-=d,b[j]-=d;
			if(!b[j]) j++;
			if(!a[i]) break;
		}
	}
	cout<<ans<<"\n";
}
signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	int _=1;
	cin>>_;
	while(_--) solve();
	return 0;
}