#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 a,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;
    int now = 0;
    for (int i = n - 1; 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;
        }
    }
    if(b[n-1]>0)
    {
        havb[n-1]=true;
        cnt_n1+=b[n-1];
        b[n-1]=0;
    }
//    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;
}