#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];
i64 ta[maxn],tb[maxn];
ll suma,sumb;
void solve()
{
    cin>>m;
    int n=m; suma=sumb=0;
    for(int i=0;i<m;++i) cin>>a[i],suma+=ta[i]=a[i];
    for(int i=0;i<m;++i) cin>>b[i],sumb+=tb[i]=b[i];
    int maxa,maxb;
    // printf("suma=%lld sumb=%lld\n",suma,sumb);
    if(suma>sumb)
    {
        for(int i=0;i<m;++i) swap(a[i],b[i]);
        swap(suma,sumb);
    }
    a[0]+=sumb-suma;
    for(int i=m-1;i>=0;--i)
        if(a[i]) 
        {
            maxa=i;
            break;
        }
    for(int i=m-1;i>=0;--i)
        if(b[i]) 
        {
            maxb=i;
            break;
        }
    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;
    }
    for(int i=m-maxb;i<m;++i)
        if(a[i]) flag=1;
    for(int i=m-maxa;i<m;++i)
        if(b[i]) flag=1;
    cout<<(flag?ans:(flag2==0?0:ans-1))<<endl;
}
int main()
{
    // ios::sync_with_stdio(0);
    // cin.tie(0); cout.tie(0);
    int t=1;
    cin>>t;
    while(t--) solve();
    return 0;
}