#include <bits/stdc++.h>
using namespace std;

#define int long long
#define rep(a, b, c) for (int a = b; a <= c; ++a)

int n;
int a[500005];
int b[500005];
void init()
{
    cin>>n;
    int ca=0,cb=0;
    for(int i=0;i<n;i++)
    {
        cin>>a[i];
        ca+=a[i];
    }
    for(int i=0;i<n;i++)
    {
        cin>>b[i];
        cb+=b[i];
    }
    if(ca<cb)
    {
        for(int i=0;i<n;i++) swap(a[i],b[i]);
    }
    //pre 0 in b,ca>cb
    return;
}

bool hava[500005],havb[500005];
void solve()
{
    for(int i=0;i<=n;i++) hava[i]=havb[i]=false;
    int cnt_n1=0;
    bool hav_mplus=false;
    if(a[n-1]>0)
    {
        cnt_n1=a[n-1];
        havb[0]=true;
    }
    int now=1;
    for(int i=n-2;i>=0;i--)
    {
        now=max(now,(n-1)-i);
        while(a[i]>0&&now<=n-1)
        {
            if(b[now]==0)
            {
                now++;
                continue;
            }
            if(i+now>=n) hav_mplus=true;
            int v=min(a[i],b[now]);
            cnt_n1+=v;
            a[i]-=v;
            b[now]-=v;
            havb[now]=true;
        }
    }
    assert(b[n-1]==0);
    if(hav_mplus==true)
    {
        cout<<cnt_n1<<'\n';
        return;
    }
    int r=-1;
    for(int i=n-1;i>=0;i--)
    {
        if(b[i]>0)
        {
            r=i;
            break;
        }
    }
    for(int i=r-1;i>=0;i--)
    {
        if(havb[i]==true)
        {
            cout<<cnt_n1<<'\n';
            return;
        }
    }
    int hav_diff=0;
    for(int i=0;i<=n-1;i++)
    {
        if(havb[i]==true) hav_diff++;
    }
    if(hav_diff>=2) cout<<cnt_n1-1<<'\n';
    else cout<<0<<'\n';
    return;
}

signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    int t = 1;
    cin >> t;
    while (t--)
    {
        init();
        solve();
    }
    return 0;
}