#include <bits/stdc++.h>
#define int long long

#define F(i, a, b) for (int i = (a); i <= (b); i++)
#define dF(i, a, b) for (int i = (a); i >= (b); i--)
using namespace std;

typedef long long ll;
typedef pair<int, int> pii;

const int N = 500005, M = (N << 1), inf = 1e16, mod = 1e9 + 7;
int n, m, a[N], b[N], c[N], d[N];
void solve(int TC) {
	cin >> m;
	int mxa = 0, mxb = 0;
	F(i, 0, m - 1) {
		cin >> a[i], c[i] = 0;
		if (a[i]) mxa = i;
	}
	F(i, 0, m - 1) {
		cin >> b[i], d[i] = 0;
		if (b[i]) mxb = i;
	}
	if (mxa + mxb < m) {
		cout << "0\n";
		return;
	}
	a[0] = b[0] = inf;
	int cnt = 0, jin = 0;
	F(i, 0, m - 1) {
		int x = min(a[i], b[m - 1 - i]);
		a[i] -= x, b[m - 1 - i] -= x;
		cnt += x;
		if (x) c[i] = d[m - 1 - i] = 1;
	}
	dF(i, m - 2, 0) c[i] |= c[i + 1], d[i] |= d[i + 1];
	for (int i = m - 1, j = 1; ~i ; --i) {
		while (a[i] && i + j >= m && j < m) {
			int x = min(a[i], b[j]);
			a[i] -= x, b[j] -= x, jin += x;
			if (!b[j]) j++;
		}
	}
	if (jin) {
		cout << jin + cnt << '\n';
	} else {
		int flag = 0;
		F(i, 1, m - 1) if (a[i] && d[m - i] || b[i] && c[m - i]) flag = 1;
		cout << cnt - 1 + flag << '\n';
	}
}
signed main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0), cout.tie(0);
	int T;
	cin >> T;
	for (int i = 1; i <= T; i ++) {
		solve(i);
	}
	return 0;
}