#include <bits/stdc++.h>
using namespace std;
using int64 = long long;
void Solve() {
    int m, f = 1; cin >> m; vector<int64> a(m), b(m);
    int64 sa = 0, sb = 0, xa = m - 1, xb = m - 1, ans = 0;
    for(int64 &x : a) cin >> x, sa += x; while(~xa && !a[xa]) --xa;
    for(int64 &x : b) cin >> x, sb += x; while(~xb && !b[xb]) --xb;
    if(xa + xb < m) return puts("0"), void();
    sa > sb ? b[0] += sa - sb : a[0] += sb - sa;
    for(int i = 0, j = m - 1; i < m; ++i)
        while(a[i] && i + j >= m - 1) {
            if(!b[j]) { --j; continue; }
            const int w = min(a[i], b[j]);
            f &= i + j < m, a[i] -= w, b[j] -= w, ans += w;
        }
    for(int i = 1; i < xb; ++i) f &= !a[m - i];
    for(int i = 1; i < xa; ++i) f &= !b[m - i]; printf("%lld\n", ans - f);
}
int main() {
    cin.tie(0)->sync_with_stdio(0);
    int T; cin >> T; while(T--) Solve();
}