#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, sa = 0, sb = 0;
	F(i, 0, m - 1) {
		cin >> a[i], c[i] = 0, sa += a[i];
		if (a[i]) mxa = i;
	}
	F(i, 0, m - 1) {
		cin >> b[i], d[i] = 0, sb += b[i];
		if (b[i]) mxb = i;
	}
	if (mxa + mxb < m) {
		cout << "0\n";
		return;
	}
	if (sa > sb) b[0] += sa - sb;
	else a[0] += sb - sa;

	int cnt = 0, flag = 1;
	dF(i, m - 2, 0) c[i] |= c[i + 1], d[i] |= d[i + 1];

	for (int i = m - 1, j = 0; ~i ; --i) {
		while (i + j < m - 1 && j < m) j++;
		while (a[i] && i + j >= m - 1 && j < m) {
			int x = min(a[i], b[j]);
			if (i + j >= m) flag = 0; 
			a[i] -= x, b[j] -= x, cnt += x;
			if (!b[j]) j++;
		}
	}
	
	F(i, 1, m - 1) if (a[m - i] || b[m - i]) flag = 0;

	cout << cnt - flag << endl;
}
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;
}

// g++ x.cpp -o a -O2 -std=c++14 -fsanitize=undefined,address