#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 double PI = acosl(-1.0);
const double eps = 1e-8;
const int MOD = 1e9 + 7;

int a[N], b[N], bei[N];
int m;
void solve()
{
    int ans = 0;
    scanf("%d", &m);
    int suma = 0, sumb = 0;
    int ma = 0, mb = 0;
    for (int i = 0; i < m; i++) {
        scanf("%d", &a[i]);
        suma += a[i];
        if (a[i]) ma = max(ma, i);
    }
    for (int i = 0; i < m; i++) {
        scanf("%d", &b[i]);
        sumb += b[i];
        if (b[i]) mb = max(mb, i);
    }
    // if (sumb > suma) {
    //     int mid;
    //     for (int i = 0; i < m; i++) {
    //         mid = a[i];
    //         a[i] = b[i];
    //         b[i] = mid;
    //     }
    //     mid = suma;
    //     suma = sumb;
    //     sumb = mid;
    // }
    for (int i = 0; i < m; i++) bei[i] = a[i];
    b[0] += (suma - sumb);
    int f = 0;
    int t = m - 1;
    int r = m - 1;
    for (int i = 0; i < m; i++) {
        while (a[i] >= b[r] && i + r >= t && r >= 0) {
            if (i + r > t) f = 1;
            ans += b[r];
            a[i] -= b[r];
            r--;
        }
        if (r >= 0 && a[i] < b[r] && i + r >= t) {
            if (i + r > t && a[i]) f = 1;
            ans += a[i];
            b[r] -= a[i];
            a[i] = 0;
        }
    }
    int x = -1;
    for (int i = 0; i < m; i++) {
        if (bei[i] > a[i] && x == -1) x = i;
        if (x != -1 && a[i] > 0 && i > x) f = 1;
    }
//    cout<<ans<<endl<<endl;
    if (!f && ma + mb >= m) ans--;
    else if (!f) ans = 0;
    printf("%lld\n", ans);
}

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