#include<bits/stdc++.h>
#define rep(i, j, k) for(int i=j;i<=k;i++)
#define rep1(i, j, k) for(int i=k;i>=j;i--)
#define ll long long
using namespace std;

const int N=5e5+5;
int T, m, a[N], b[N], mx[2];
ll s[2], ans;

int main(){
	
	cin>>T;
	while(T--){
		cin>>m; 
		mx[0]=mx[1]=ans=s[0]=s[1]=0;
		
		rep(i, 0, m-1){
			cin>>a[i]; s[0]+=a[i];
			if(a[i]) mx[0]=i;
		}
		rep(i, 0, m-1){
			cin>>b[i]; s[1]+=b[i];
			if(b[i]) mx[1]=i;
		}
		if(mx[0]+mx[1]<m){puts("0"); continue;}
		
		if(s[0]>s[1]) b[0]+=s[0]-s[1];
		else a[0]+=s[1]-s[0];
		
		int j=m-1; bool p=1;
		rep(i, 0, m-1){
			while(a[i] && i+j>=m-1){
				if(!b[j]){--j; continue;}
				int del=min(a[i], b[j]);
				a[i]-=del, b[j]-=del, ans+=del, p&=(i+j==m-1);
			}
		}
		rep(i, 1, mx[0]) p&=!a[m-i];
		rep(i, 1, mx[1]) p&=!b[m-i];
		cout<<ans-p<<endl;
	}
	
	return 0;
}
/*

恩偶挨批莫尼塞梯 

*/