#include <bits/stdc++.h>
using namespace std;

#define int long long
const int INF = 1e16;

void solve() {
	int n; cin >> n;
	vector<int> a(n), b(n);
	for (int &i: a) cin >> i;
	for (int &i: b) cin >> i;
	a[0] = b[0] = INF;

	// is carrying even possible?
	{
		bool answer_z = 1;
		int has_b = 0, has_a = 0;
		for (int i = 1, j = n-1; i < n; i++, j--) {
			if (b[j]) has_b = 1;
			if (has_b && a[i] > 0) {
				answer_z = 0; break;
			}
			if (a[j]) has_a = 1;
			if (has_a && b[i] > 0) {
				answer_z = 0; break;
			}
		}
		if (answer_z) {
			cout << "0\n";
			return;
		}
	}

	// how many carries are there? any overcarries?
	int ans = 0; bool overcarry = 0;
	for (int i = 0, j = n-1; i < n; i++) {
		while (a[i] > 0) {
			if (i+j < n-1) break;
			int mn = min(a[i], b[j]);
			a[i] -= mn; b[j] -= mn; ans += mn;

			if (mn > 0 && i+j >= n) overcarry = 1;
			if (b[j] == 0) j--;
		}
	}

	if (overcarry) {
		cout << ans << '\n';
		return;
	} else {
		cout << ans-1 << '\n';
		return;
	}
}

signed main() {
	ios::sync_with_stdio(0); cin.tie(0);
	
	int t; cin >> t;
	while (t--) {
		solve();
	}
	
	return 0;
}