#include<bits/stdc++.h>
#define endl '\n'
using i64 = long long;
using ll = long long;
using namespace std;
constexpr int N = 5e5 + 10;

int m;
int a[N],b[N];
void solve(){
    cin >> m;
    for(int i=0; i<m; ++i)cin >> a[i];
    for(int i=0; i<m; ++i)cin >> b[i];
    a[m] = b[m] = 0;
    ll res = 0;
    int t = 0;
    auto cal = [&](){
        for(int i=m-1, j=1; i>0; --i){
            if(!a[i])continue;
            if(b[0] && i + t >= m){
                int d = min(a[i], b[0]);
                b[0] -= d;
                a[i] -= d;
                res += d;
                ++i;
                t = 1;
                continue;
            }
            while(j < m && (i + j + t < m || !b[j]))++j;
            if(!b[j])break;
            if(t == 0){
                t = 1;
                ++res;
                a[i]--, b[j]--;
                ++i;
                continue;
            }
            int d = min(a[i], b[j]);
            res += d;
            a[i] -= d;
            b[j] -= d;
            t = 1;
            if(a[i])++i;
        }
    };
    cal();
    for(int i=0; i<m; ++i)swap(a[i], b[i]);
    cal();
    if(a[m-1] && t)res += a[m-1];
    if(b[m-1] && t)res += b[m-1];
    cout << res << endl;
}

signed main(){
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    int t = 1;
    cin >> t;
    while(t--)solve();
    return 0;
}