#include <bits/stdc++.h>

using namespace std;

int main() {
  cin.tie(0)->sync_with_stdio(0);
  for (int tc = (cin >> tc, tc); tc--; ) {
    int m; cin >> m;
    vector<int64_t> a(m), b(m);
    int maxa = -1, maxb = -1;
    for (int i = 0; i < m; ++i) cin >> a[i], maxa = a[i]? i: maxa;
    for (int i = 0; i < m; ++i) cin >> b[i], maxb = b[i]? i: maxb;
    a[0] = b[0] = 1e18;
    int64_t ans = 0;
    bool carry = 0;
    for (int i = m - 1, j = 0; j < m && i > -1; i -= !a[i], j += !b[j] || i + j < m - 1) {
      int64_t c = min(a[i], b[j]);
      carry |= c && i + j >= m;
      ans += c, a[i] -= c, b[j] -= c;
    }
    for (int i = m; i--; ) carry |= a[i] && i + maxb >= m;
    for (int i = m; i--; ) carry |= b[i] && i + maxa >= m;
    if (!carry) --ans, carry |= maxa + maxb >= m;
    cout << (carry? ans: 0) << '\n';
  }
}