#include<bits/stdc++.h>
#define N 1000010
#define ll long long
using namespace std;
int n,T;
ll a[N],b[N];

int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
    cin>>T;
    while(T--){
        cin>>n;
        int fa=0,fb=0;
        for(int i=0;i<n;i++){
            cin>>a[i];
            if(a[i]) fa=i;
        }
        for(int i=0;i<n;i++){
            cin>>b[i];
            if(b[i]) fb=i;
        }
        a[0]=b[0]=1e18;
        if(fa+fb<n){
            cout<<"0\n";
            continue;
        }
        int pi=0;
        ll sum=0,fz=0;
        for(int i=n-1;i>=0;i--){
            if(pi+i<n-1) pi++;
            while(pi<n&&a[pi]<=b[i]){
                if(a[pi]&&pi+i>=n) fz=1;
                b[i]-=a[pi];
                sum+=a[pi];
                a[pi]=0;
                pi++;
            }
            if(a[pi]>b[i]){
                if(b[i]&&pi+i>=n) fz=1;
                sum+=b[i],a[pi]-=b[i],b[i]=0;
            }
        }
        cout<<sum+fz-1<<'\n';
    }
    return 0;
}