/*YYC is Thinking Here*/
#include<bits/stdc++.h>
#define mids(l,r) const auto mid = (l + r) >> 1
#define lb(x) (x&-x)
#define ls (x<<1)
#define rs (ls|1)
#define int long long
#define pii pair<int,int>
#define inf 0x3f3f3f3f3f3f3f3f
using namespace std;
const int maxn = 1e6+10;
int a[maxn],b[maxn];
int n,x,y,ans;
void sol(){
	cin>>n;
	for(int i = 1;i <= n;++i) cin>>a[i];
	for(int i = 1;i <= n;++i) cin>>b[i];
	ans = x = y = 0;
	//x -1; y +1
	for(int i = 1;i <= n;++i) {
		// deb(i,ans,x,y);
		if(b[i] == 0) {
			if(a[i] - x > 0) {
				ans += a[i] - x;
				x = a[i];
			}
		} else {
			if(a[i] == 0) return cout<<"-1\n",void();
			if(a[i] - x <= 0) x = a[i] - 1;
			if(a[i] - x + y > b[i]) {
				y -= min(y, a[i] - x + y - b[i]);
				int v = a[i] - x + y - b[i];
				x += v, ans += v;
			}
			if(a[i] - x + y < b[i]) {
				x -= min(x, b[i] - (a[i] - x + y));
				int v = b[i] - (a[i] - x + y);
				y += v, ans += v;
			}
		}
		// deb(i,ans,x,y);
	}
	cout<<ans<<'\n';
}
signed main() {
	// freopen("game.in","r",stdin);
	// freopen("game.out","w",stdout);
	ios::sync_with_stdio(0),cin.tie(0);
	int T;cin>>T;while(T--)sol();
}

/*
* I love it all
* Go forward,move forward !
*/