#include<bits/stdc++.h>
#define int long long
#define pb push_back
#define debug(x) cerr <<#x <<" = " << x << endl
#define fi first
#define se second
using namespace std;
const int N = 5e5 +10;
int T= 1;

int n, a[N], b[N], tem[N], c[N];

void solve(){
	cin >> n;
	int m = n;
	int la = 0, lb = 0;
	for (int i = 0; i < n; i ++) cin >> a[i], la += a[i], c[i] = 0;
	for (int i = 0; i < n; i ++) cin >> b[i], lb += b[i];
	if (lb > la){
		for (int i = 0; i < n; i ++) tem[i] = a[i];
		for (int i = 0; i < n; i ++) a[i] = b[i], b[i] = tem[i];
	}
	int p = 0, s = 0, fl = 0, kid = 0;
    for (int i = n - 1; i >= 0; i --){
    	p = max(p, n - 1 - i);
    	while (b[i] && p < n){
    		if (p + i >= m) fl = 1;
    		int t = min(b[i], a[p]);
    		if (t) kid ++;
    		b[i] -= t, a[p] -= t, s += t;
    		c[i] += t;
    		if (!a[p]) p ++;
    	}
    }
    int cc = 0;
    for (int i = 1; i < n; i ++){
    	int r = m - i;
    	if (c[r]) cc = 1;
    	if (cc && a[i]){
    		fl = 1;
    		a[i] --;
    		break;
    	}
    }
    if (a[n - 1] || b[n - 1]) s += max(a[n - 1], b[n - 1]);
    if (fl) return void(cout << s << endl);
    if (kid > 1) cout << s - 1 << endl;
    else cout << 0 << endl;
}

signed main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);

	cin >> T;
	while(T --) solve();

	return 0;
}