#include<bits/stdc++.h>
#define rep(i,j,k) for(int i=j;i<(k);++i)
#define all(i) (i).begin(),(i).end()
#define sz(i) (int)(i).size()
using namespace std;

typedef long long ll;

typedef vector<int> vi;

vi first, second, links;

int next(int i) {
    if (links[i] == i) return i;
    return links[i] = next(links[i]);
}

int main() {
    int t;
    cin >> t;

    while (t--) {
        int m;
        cin >> m;
        first.resize(m);
        second.resize(m);
        links.resize(m+1);
        iota(all(links), 0);
        ll diff = 0;
        rep(i,0,m) {
            cin >> first[i];
            diff += first[i];
        }
        rep(i,0,m) {
            cin >> second[i];
            diff -= second[i];
        }

        if (diff < 0) first[0] += 1000000000;
        else second[0] += 1000000000;

        ll ans = 0;
        int dec = 1;

        rep(i,0,m) {
            int cur = first[i];
            int it = m-1-i;
            it=next(it);
            while (cur && it<m) {
                if (it > m-1-i) dec=0;
                int sub = min(cur, second[it]);
                // cout << cur << ' ' << second[it] << ' ' << sub << endl;
                ans += sub;
                cur -= sub;
                second[it] -= sub;
                if (second[it] <= 0) {
                    links[it] = it+1;
                    it=next(it);
                }
                else break;
            }
        }

        rep(i,0,m) if (first[i]) {
            int it = m-i; // 1 bigger
            it=next(it);
            // cout << i << ' ' << it << ' '<< first[i] << ' '<< second[it] << endl;
            if (it < m) { // could have used one bigger
                dec=0;
                break;
            }
        }

        ans=max(0LL,ans-dec);

        printf("%lld\n",ans);

        // break;
    }

    return 0;
}