#include <bits/extc++.h>
using namespace std;
#define C const
#define CE constexpr
#define TL template
#define TN typename
#define OP operator
#define pb push_back
#define ft first
#define sd second
#define mi (l+(r-l)/2)
#define TTT TL<TN T>
#define BE(v) v.begin(), v.end()
#define U unsigned
#define VD void
#define I int
#define LL long long
#define D double
using STR = string;
using PII = pair<I, I>;
TTT using V = vector<T>;

#define FORX(v) for(auto& x:v)
#define FOR(i,b,e) for(I i = b, _e = e;i<_e;++i)
#define FORR(i,b,e) for(I i = b, _e = e;i>_e;--i)
#define FUNC(T,f,...) function<T(__VA_ARGS__)> f = [&](__VA_ARGS__)->T

TTT VD setmin(T& a, C T& b){if(b<a)a=b;}
TTT VD setmax(T& a, C T& b){if(a<b)a=b;}

VD test()
{
    I m; cin>>m;
    V<I> a(m), b(m);
    FORX(a)cin>>x;
    FORX(b)cin>>x;
    a[0] = 1e9, b[0] = 1e9;
    I l = 0, r = m-1;
    LL cnt[2] = {0,0};
    I mxl = -1e9, mxr = -1e9;
    while(l<m&&r>=0)
    {
        I num = min(a[l], b[r]);
        if(num)setmax(mxr,r), setmax(mxl,l);
        a[l]-=num; b[r]-=num;
        cnt[l+r>=m]+=num;
        if(a[l]==0)++l;
        else if(b[r]==0)
        {
            --r;
            if(l+r<m-1)++l;
        }
    }
    if(cnt[1])
    {
        cout<<cnt[0]+cnt[1]<<'\n';
    }
    else
    {
        I mxa = -1e9;
        FOR(i,0,m)if(a[i]>0)setmax(mxa, i);
        if(mxa+mxr>=m)cout<<cnt[0]<<'\n';
        else if(mxl+mxr>=m)cout<<cnt[0] - 1<<'\n';
        else cout<<"0\n";

    }
}

I main()
{
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    if(fopen("test.in","r"))
    {
        freopen("test.in","r",stdin);
        freopen("test.out","w",stdout);
    }
    I t = 1;
    cin >> t;
    while(t--)test();
    return 0;
}