#include<cstdio>
typedef long long ll;
inline ll read(){
	ll x=0;
	int f=0,ch=0;
	while(ch<48||ch>57) f=(ch=='-'),ch=getchar();
	while(ch>47&&ch<58) x=(x<<3)+(x<<1)+(ch&15),ch=getchar();
	return f?-x:x;
}
inline void write(ll x,char end='\n'){
	if(x==0){
		putchar('0');
		putchar(end);
		return;
	}
	if(x<0) putchar('-'),x=-x;
	int ch[40]={0},cnt=0;
	while(x){
		ch[cnt++]=(int)(x%10);
		x/=10;
	}
	while(cnt--) putchar(ch[cnt]+48);
	putchar(end);
}
inline ll max(ll x,ll y){return x>y?x:y;}
inline ll min(ll x,ll y){return x<y?x:y;}
const ll inf=1e15;
const int N=5e5+5;
ll a[N],b[N],m;
inline void solve(){
	m=read();
	ll sa=0,sb=0;
	for(int i=0;i<m;++i) a[i]=read(),sa+=a[i];
	for(int i=0;i<m;++i) b[i]=read(),sb+=b[i];
	a[0]+=sb-sa,b[0]+=sa-sb;
	ll t=min(a[0],b[0]);
	a[0]-=t,b[0]-=t;
	int flag=0;
	ll now=0,can=0;
	for(int i=1;i<m;++i){
		now+=b[m-i];
		if(now&&a[i]){
			flag=1;
			ll t=min(now,a[i]);
			now-=t;
			can+=t;
		}
	}
	if(!flag){
		puts("0");
		return;
	}
	flag=0;
	ll ans=0;
	int l=m-1;
	int mna=-1,mnb=-1;
	for(int i=0;i<m;++i){
		while(a[i]&&l>=m-i-1){
			if(!b[l]){
				--l;
				continue;
			}
			int t=min(a[i],b[l]);
			if(mna==-1) mna=i;
			mnb=l;
			if(i+l>=m) flag=1;
			ans+=t;
			a[i]-=t;
			b[l]-=t;
			if(!b[l]) --l;
		}
	}
	ans+=a[m-1]+b[m-1];
	if(!flag){
		int taga=-1,tagb=-1;
		for(int i=mna+1;i<m;++i){
			if(a[i]){
				taga=i;
				break;
			}
		}
		for(int i=mnb+1;i<m;++i){
			if(b[i]){
				tagb=i;
				break;
			}
		}
		if(taga==-1&&tagb==-1) ans--;
		else if(taga==-1){
			if(tagb==m-1) ans--;
		}
		else if(tagb==-1){
			if(taga==m-1) ans--;
		}
		else{
			if(taga==m-1&&tagb==m-1) ans--;
		}
	}
	write(ans,'\n');
}
int main(){
	int T=read();
	while(T--) solve();
	return 0;
}