#include<iostream>
#include<cstdio>
#include<algorithm>
#define int long long
using namespace std;
const int MX=500050;
const int inf=1e15;

int T, N;
int ar[MX], br[MX], suf[MX];
int read()
{
    int r=0, f=1; char ch=getchar();
    while(ch<'0'||ch>'9') {if(ch=='-') f=-1; ch=getchar();}
    while(ch>='0'&&ch<='9') {r=r*10+ch-'0'; ch=getchar();}
    return r*f;
}
signed main()
{
    // freopen("testdata.in","r",stdin);
    T=read();
    while(T--)
    {
        N=read();
        int sa=0, sb=0;
        for(int i=0;i<N;i++) ar[i]=read(), sa+=ar[i];
        for(int i=0;i<N;i++) br[i]=read(), sb+=br[i];
        sa-=ar[N-1]; sb-=br[N-1];
        int sum=0, suf=0, tag=1;
        for(int i=1;i<N-1;i++)
        {
            suf+=br[N-1-i];
            int num=min(ar[i],suf);
            suf-=num;
            sum+=num; 
            if(suf!=0) tag=0;
        }
        suf=0;
        for(int i=1;i<N-1;i++)
        {
            suf+=ar[N-1-i];
            int num=min(br[i],suf);
            suf-=num;
            sum+=num; 
            if(suf!=0) tag=0;
        }
        sum/=2;
        if(sa-sum>=br[N-1]||sb-sum>=ar[N-1]) 
        {
            sum+=ar[N-1]+br[N-1];
            if(sa-sum>=br[N-1]&&sa-sum!=ar[0]) tag=0;
            if(sb-sum>=ar[N-1]&&sb-sum!=br[0]) tag=0;
        }
        else
        {
            sum+=max(sa-sum+br[N-1],sb-sum+ar[N-1]);
            tag=0;
        }
        cout << sum-tag << '\n';
    }
    return (0-0);
}