#include <bits/stdc++.h>
#define ll long long
#define pb push_back

using namespace std;

int main()
{
    ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);

	int t = 1;
	cin >> t;
    while(t-->0)
    {
        int n;
        cin >> n;

        vector<ll> a(n), b(n);
        for(int i=0; i<n; i++) cin >> a[i];
        for(int i=0; i<n; i++) cin >> b[i];

        ll suma = 0, sumb = 0;
        for(int i=0; i<n; i++)
        {
            suma += a[i];
            sumb += b[i];
        }

        if(suma < sumb) a[0] += sumb - suma;
        else b[0] += suma - sumb;

        bool ok = false;
        int index1 = n-1, index2 = 0;
        ll ans = 0;

        vector<ll> p, q(n, 0);

        for(index1 = n-1; index1 >= 0; index1--)
        {
            index2 = max(index2, n - 1 - index1);
            while(index2 != n && a[index1] > 0)
            {
                ll m = min(a[index1], b[index2]);
                //cout << "!! " << m << " " << index1 << "\n";
                if(m > 0) p.pb(index1);
                a[index1] -= m;
                b[index2] -= m;
                ans += m;
                if(index1 + index2 >= n) ok = true;
                if(b[index2] == 0) index2++;
            }
        }

        reverse(p.begin(), p.end());
        int k = p.size(), now = 0;
        ll sum = 0;
        for(int i=0; i<n; i++)
        {
            while(now < k && p[now] == i)
            {
                //cout << "! " << p[now] << " " << sum << "\n";
                if(sum > 0) ok = true;
                now++;
            }
            sum += b[n - 1 - i];
        }

        cout << max(0LL, ans - 1 + ok) << "\n";
    }
}