#include <bits/stdc++.h>

using namespace std;

const int N = 5e5 + 5;

long long a[N], b[N], ta[N], tb[N];

signed main() {
    int T; scanf("%d", &T);
    while (T--) {
        int n; scanf("%d", &n);
        for (int i = 0; i < n; ++i) scanf("%lld", &a[i]), ta[i] = a[i];
        for (int i = 0; i < n; ++i) scanf("%lld", &b[i]), tb[i] = b[i];
        a[0] = 1e18, b[0] = 1e18;
        long long res = 0;
        int flg = 0;
        int mxa = 0, mxb = 0;
        for (int i = 0, j = n - 1; i < n; ) {
            while (i < n && !a[i]) ++i;
            while (~j && !b[j]) --j;
            if (i == n || !~j) break;
            if (i + j >= n - 1) {
                if (i + j >= n) flg = 1;
                long long v = min(a[i], b[j]);
                mxa = max(mxa, i), mxb = max(mxb, j);
                a[i] -= v, b[j] -= v, res += v;
            } else ++i;
        }
        if (flg) printf("%lld\n", res);
        else {
            int flag = 0;
            for (int i = 0; i < n; ++i) {
                if (a[i] && i + mxb >= n) flag = 1;
                if (b[i] && i + mxa >= n) flag = 1;
            }
            if (flag) {
                printf("%lld\n", res);
                continue;
            }
            int mx1 = 0, mx2 = 0;
            for (int i = n - 1; ~i; --i) if (ta[i]) {mx1 = i; break;}
            for (int i = n - 1; ~i; --i) if (tb[i]) {mx2 = i; break;}
            if (mx1 + mx2 >= n) printf("%lld\n", res - 1);
            else puts("0");
        }
    }
    return 0;
}