#include <bits/stdc++.h>
#define int long long
#define debug cerr << "[" << __LINE__ << "] "
#define SZ(x) (int) x.size() - 1
#define all(x) x.begin(), x.end()
#define ms(x, y) memset(x, y, sizeof x)
#define F(i, x, y) for (int i = (x); i <= (y); i++)
#define DF(i, x, y) for (int i = (x); i >= (y); i--)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
template <typename T> void chkmax(T& x, T y) { x = max(x, y); }
template <typename T> void chkmin(T& x, T y) { x = min(x, y); }
template <typename T> void read(T &x) {
	x = 0; int f = 1; char c = getchar();
	for (; !isdigit(c); c = getchar()) if (c == '-') f = -f;
	for (; isdigit(c); c = getchar()) x = x * 10 + c - '0';
	x *= f;
}
const int N = 5e5 + 10;
int n, a[N], b[N], s1, s2;
bool check(int x) {
	vector <pair <int, int>> v1, v2;
	int t = x;
	DF(i, n - 1, 0) if (a[i]) {
		int k = min(t, a[i]);
		v1.emplace_back(i, k);
		t -= k;
		if (!t) break;
	}
	t = x;
	DF(i, n - 1, 0) if (b[i]) {
		int k = min(t, b[i]);
		v2.emplace_back(i, k);
		t -= k;
		if (!t) break;
	}
	reverse(all(v2));
	bool flag = false;
	for (int i = 0, j = 0; i <= SZ(v1); ) {
		int t = min(v1[i].second, v2[j].second);
		if (v1[i].first + v2[j].first >= n) flag = true;
		if (v1[i].first + v2[j].first < n - 1) return false;
		if (!(v1[i].second -= t)) i++;
		if (!(v2[j].second -= t)) j++;
	}
	return flag;
}
void zhk() {
	read(n);
	s1 = s2 = 0;
	F(i, 0, n - 1) read(a[i]), s1 += a[i];
	F(i, 0, n - 1) read(b[i]), s2 += b[i];
	a[0] += 1e9, b[0] += 1e9;
	s1 += 1e9, s2 += 1e9;
	int l = 0, r = min(s1, s2) + 1;
	while (l + 1 < r) {
		int mid = (l + r) >> 1;
		if (check(mid)) l = mid;
		else r = mid;
	}
	// debug << s1 << " " << s2 << endl;
	cout << l << '\n';
}
signed main() {
	int _;
	read(_);
	while (_--) zhk();
	return 0;
}