#include <bits/stdc++.h>

using namespace std;
using LL=long long;

int main()
{
	cin.tie(0)->sync_with_stdio(false);
	int _=1;
	cin>>_;
	while (_--){
		int n;
		cin>>n;
		vector <LL> a(n+10,0),b(n+10,0);
		LL fin=0;
		for (int i=0;i<n;i++) cin>>a[i],fin+=a[i];
		for (int i=0;i<n;i++) cin>>b[i],fin-=b[i];
		if (fin>0) b[0]+=fin;
		else a[0]-=fin;
		vector <LL> c=a,d=b;
		LL ans=0,r=n-1,bg=0;
		for (int i=0;i<n;i++){
			while (r>=0 and r+i>=n-1 and c[i]){
				if (d[r]>c[i]){
					if (r+i>=n) bg=1;
					ans+=c[i];
					d[r]-=c[i];
					c[i]=0;
				}
				else{
					if (r+i>=n and d[r]) bg=1;
					ans+=d[r];
					c[i]-=d[r];
					d[r]=0;
					r--;
				}
			}
		}
		if (bg) cout<<ans<<'\n';
		else{
			int id=0;
			for (int i=n-1;i>=1;i--){
				if (a[i]){
					id=i;
					break;
				}
			}
			bool fd=0;
			for (int i=n-1;i>=0;i--){
				if (id+i>=n and b[i]){
					fd=1;
					break;
				}
			}
			if (fd) cout<<ans-1<<'\n';
			else cout<<0<<'\n';
		}
	}
}