#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define ull unsigned long long
#define mk make_pair
#define lowbit(x) (x&(-x))
#define pb emplace_back
#define pr pair<int,int>
#define let const auto
#define all(A) A.begin(),A.end()
const int N=5e5+5;
int read(){
	int x=0,f=1; char c=getchar();
	while(('0'>c||c>'9')&&c!='-') c=getchar();
	if(c=='-') f=0,c=getchar();
	while('0'<=c&&c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar();
	return f?x:-x;
}
void solve(){
	int m=read();
	vector <int> a(m),b(m);
	for(auto &o:a) o=read();
	for(auto &o:b) o=read();
	int posa=0,posb=m-1;
	ll ans=0,ans2=0;
	ll sa=accumulate(all(a),0ll),sb=accumulate(all(b),0ll);
	if(sa<sb) a[0]+=sb-sa;
	else b[0]+=sa-sb;
	int lasa=m-1,lasb=m-1;
	while(lasa>0&&!a[lasa]) lasa--;
	while(lasb>0&&!b[lasb]) lasb--;
	if(lasa+lasb<m) return puts("0"),void();
	int p=-1,yes=0;
	while(posa<m&&posb>=0){
		int cur=min(a[posa],b[posb]);
		if(posa+posb>=m) ans+=cur;
		else if(posa+posb==m-1) ans2+=cur;
		else{
			posa++;
			continue;
		}
		if(cur>0&&p==-1) p=posa;
		a[posa]-=cur,b[posb]-=cur;
		if(!a[posa]) posa++;
		if(!b[posb]) posb--;
	}
	if(~p&&p<m-1&&*max_element(a.begin()+p+1,a.end())>0) yes=1;
	if(ans) yes=1;
	printf("%lld\n",ans+ans2-(!yes));
}
int main(){
	int T=read();
	while(T--) solve();
	return 0;
}