#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef ll i64;
typedef __int128 i128;
constexpr int maxn=5e5+9;
int m;
i64 a[maxn],b[maxn];
ll suma,sumb;
map<ll,int> Maa;
void solve()
{
    cin>>m;
    int n=m; suma=sumb=0;
    for(int i=0;i<m;++i) cin>>a[i],suma+=a[i];
    for(int i=0;i<m;++i) cin>>b[i],sumb+=b[i];
    if(suma<sumb) a[0]+=sumb-suma;
    if(suma>sumb) b[0]+=suma-sumb;
    int ptr=m-1;
    ll ans=0;
    int flag=0,flag2=0;
    ll ss=0;
    for(int i=0;i<m;++i)
    {
        ss+=b[m-i];
        if(ss && a[i]) { flag2=1; break; }
    }
    for(int i=0;i<m;++i)
    {
        if(!a[i]) continue;
        while(ptr>=0 && !b[ptr]) --ptr;
        if(ptr<0) break;
        if(i+ptr>=m) flag=1;
        while(ptr>=m-1-i && a[i])
        {
            int match=std::min(a[i],b[ptr]);
            // printf("match %d of %d in a and %d in b\n",match,i,ptr);
            ans+=match;
            b[ptr]-=match;
            a[i]-=match;
            if(!b[ptr]) --ptr;
        }
        if(ptr<0) break;
    }
    cout<<(flag2==0?0:(flag==0?ans-1:ans))<<endl;
}
int main()
{
    // ios::sync_with_stdio(0);
    // cin.tie(0); cout.tie(0);
    int t=1;
    cin>>t;
    while(t--) solve();
    return 0;
}