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

#define int long long  

void solve() {
	int m;
	cin >> m;

	int sa = 0, sb = 0;
	vector<int> a(m + 1), b(m + 1);
	for (int i = 1; i <= m; i++) {
		cin >> a[i];
		sa += a[i];
	}
	for (int i = 1; i <= m; i++) {
		cin >> b[i];
		sb += b[i];
	}

	if (sa > sb) {
		b[1] += sa - sb;
	} else {
		a[1] += sb - sa;
	}

	reverse(b.begin() + 1, b.end());
	vector<int> s(m + 1);
	for (int i = 1; i <= m; i++) {
		s[i] = s[i - 1] + b[i];
	}

	vector<vector<int>> dp(m + 1, vector<int>(2, -1e18));	
	dp[0][0] = 0;
	dp[0][1] = -1e18;
	for (int i = 1; i <= m; i++) {
		dp[i][0] = dp[i - 1][0] + min(s[i] - dp[i - 1][0], a[i]);
		if (a[i] > 0 && s[i - 1] > dp[i - 1][0]) {
			dp[i][1] = dp[i - 1][0] + 1 + min(a[i] - 1, s[i] - 1 - dp[i - 1][0]);			
		}
		dp[i][1] = max(dp[i][1], dp[i - 1][1] + min(s[i] - dp[i - 1][1], a[i]));
		// cout << dp[i][0] << " " << dp[i][1] << "\n";
	}
	if (dp[m][1] < 0) {
		cout << dp[m][0] - 1 << "\n";
	} else {
		cout << dp[m][1] << "\n";	
	}
}

signed main() {  
    ios::sync_with_stdio(false);
    cin.tie(nullptr);  

    int t;
    cin >> t;
    while (t--) {
    	solve();
    }

    return 0;
}