#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];
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];
        if(sa<sb) ar[0]+=sb-sa;
        else br[0]+=sa-sb;
        sa=sb=max(sa,sb);
        int ans=0, tag=1;
        for(int i=0,j=N-1;i<N;i++)
        {
            int now=0;
            while(ar[i]>now&&j>=N-i-1) 
            {
                if(j>N-i-1) tag=0;
                int d=ar[i]-now;
                int del=min(d,br[j]);
                br[j]-=del; now+=del;
                if(!br[j]) j--;
            }
            ans+=now;
        }
        if(!ans) cout << "0\n";
        else cout << ans-tag << '\n';
    }
    return (0-0);
}