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

constexpr int N = 500010;

long long T, m, a[N], b[N];
long long ans;
bool flag;

int main() {
    scanf("%lld", &T);
    while (T--) {
        scanf("%lld", &m), ans = 0ll;
        for (int i = 0;i < m;++i)
            scanf("%lld", &a[i]);
        for (int i = 0;i < m;++i)
            scanf("%lld", &b[i]);
        a[0] = 0xf3f3f3f3f3f3f3f;
        b[0] = 0xf3f3f3f3f3f3f3f;
        int p = m-1, pp, q = m-1;
        while (p >= 0 && !a[p])
            --p;
        pp = p;
        if (p == -1) {
            puts("0");
            continue;
        }
        while (q >= 0 && !b[q])
            --q;
        if (p+q < m) {
            puts("0");
            continue;
        }
        q = m-1-p, flag = false;
        while (p >= 0) {
            // printf("#%d %d %lld\n", p, q, ans);
            while (q < m && !b[q])
                ++q;
            if (q == m)
                break;
            if (a[p]) {
                if (b[q] > a[p]) {
                    if (p+q >= m)
                        flag = true;
                    ans += a[p];
                    b[q] -= a[p];
                    a[p] = 0;
                }
                else {
                    if (p+q >= m)
                        flag = true;
                    ans += b[q];
                    a[p] -= b[q];
                    b[q] = 0;
                }
            }
            if (!a[p]) {
                if (p+q == m-1) {
                    if (b[q] && q > m-pp-1)
                        flag = true;
                    ++q;
                }
                --p;
            }
        }
        printf("%lld\n",flag?ans:(ans-1));
    }
    return 0;
}