#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef long double LD;
#define int LL
#define double LD
#define endl "\n"
typedef pair<int, int> PII;
const int N = 5e5 + 5;
const int INF = 0x3f3f3f3f;
const int inf = 0x3f3f3f3f3f3f3f3f;
const double PI = acosl(-1.0);
const double eps = 1e-8;
const int MOD = 1e9 + 7;

int a[N], b[N];
int aa[N], bb[N];
int m;
int nnn = 0;
int calc(int a[], int b[], int ma, int mb)
{
    int res = 0;
    int ca = -1, cb = -1;
    for (int i = 0; i < m; i++) {
        if (a[i] && b[m - i]) {
            ca = i;
            cb = m - i;
            break;
        }
    }
    if (ca == -1 && cb == -1) {
        if (ma + mb >= m) {
            ca = ma;
            cb = mb;
        }
    }
    if (ca != -1 && cb != -1) {
//        cout << ca << " " << cb << " " << endl;
        a[ca]--;
        b[cb]--;
        res++;
    }
    else {
        return 0;
    }
    int r = m - 1;
    int t = m - 1;
    for (int i = 0; i < m; i++) {
        while (r >= 0 && a[i] >= b[r] && i + r >= t) {
            res += b[r];
            a[i] -= b[r];
            r--;
        }
        if (r >= 0 && a[i] < b[r] && i + r >= t) {
            res += a[i];
            b[r] -= a[i];
            a[i] = 0;
        }
    }
    res += a[m - 1];
    return res;
}
void solve()
{
    nnn++;
    cin >> m;
    string x;
    int suma = 0, sumb = 0;
    int ma = 0, mb = 0;
    for (int i = 0; i < m; i++) {
        cin >> a[i];
        aa[i] = a[i];
        suma += a[i];
        if (a[i]) ma = max(ma, i);
        x += char(a[i]);
    }
    for (int i = 0; i < m; i++) {
        cin >> b[i];
        bb[i] = b[i];
        sumb += b[i];
        if (b[i]) mb = max(mb, i);
        x += (char) a[i];
    }
    if (nnn == 50)
        for (int i = 4; i < x.length(); i++) {
            cout << x[i];
        }
    int ans = calc(a, b, ma, mb);
//    for (int i = 0; i < m; i++) {
//        cout << a[i] << " " << b[i] << endl;
//    }
    ans = max(ans, calc(bb, aa, mb, ma));
//    cout << "olahfc\n";
    cout << ans << endl;
}

signed main()
{
    ios::sync_with_stdio(false), cin.tie(0);
    int _;
    cin >> _;
//    _ = 1;
    while (_--) {
        solve();
    }
    return 0;
}