#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];
    // 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);
    }
    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)
    {
        while(ptr>=0 && i+ptr>=m-1 && a[i]>=b[ptr])
        {
            // printf("match %lld of %d in a and %d in b\n",b[ptr],i,ptr);
            if(i+ptr>=m) flag=1;
            ans+=b[ptr];
            a[i]-=b[ptr]; b[ptr]=0;
            --ptr;
        }
        if(ptr>=0 && i+ptr>=m-1 && a[i])
        {
            // printf("match %lld of %d in a and %d in b\n",a[i],i,ptr);
            if(i+ptr>=m) flag=1;
            ans+=a[i];
            b[ptr]-=a[i]; a[i]=0;
        }
    }
    int tmp=-1;
    for(int i=0;i<m;++i)
        if(ta[i]>a[i]) {
            tmp=i;
            break;
        }
    for(int i=tmp+1;i<m;++i)
        if(a[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;
}