#include <bits/stdc++.h>

using namespace std;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);
	int T;
	cin >> T;
	while (T--) {
		int n;
		cin >> n;
		vector<int64_t> a(n), b(n);
		for(int i = 0; i < n; i ++) cin >> a[i];
		for(int i = 0; i < n; i ++) cin >> b[i];
		int64_t x = 0, y = 0, z = 0, w = 0, v = 0, ans = 0;
		for(int i = 0; i < n; i ++) {
			if(!a[i]) {
				if(b[i]) {
					ans = -1;
					break;
				}
			}
			else {
				if(b[i]) {
					x = min(x, a[i] - 1);
					a[i] += y - x;
					if(a[i] < b[i]) {
						int64_t t = b[i] - a[i];
						if(x < t) {
							y += t - x;
							auto k = min(v, t - x);
							v -= k, ans += t - x - k;
							t = x;
						}
						x -= t;
						int64_t s = min(t, v);
						y += s, x += s, z += t - s;
					}
					else {
						int64_t t = a[i] - b[i];
						if(y < t) { 
							ans += t - y;
							x += t - y;
							a[i] -= t - y; 
							t = y;
						}
						int64_t aa = a[i] - y - 1;
						if(aa < t) y -= t - aa, t = aa;
						y -= t;
						z += t;
					}
					z += v;
					v = 0;
					z = min(z, b[i] - 1 - y);
				}
				else {
					if(a[i] <= x) continue;
					ans += a[i] - x;
					auto k = min(z, a[i] - x);
					x += a[i] - x;
					v += k, z -= k;
				}
			}
		}
		cout << ans << '\n';
	}
	return 0;
}