#include <bits/stdc++.h>
using namespace std;
#define M 500005
using ll = long long;
int m;
ll A[M],B[M];
ll C[M],s[M];
ll f[M][3];//-1,0,+1
ll solve(){
    for(int i=0;i<=m;i++)
        C[i] = f[i][0] = f[i][1] = f[i][2]=0;
    reverse(B,B+m);
    C[0] = 0;
    ll res = 0;
    for(int i=0;i<m;i++){
        res += B[i];
        s[i] = max(res-A[i],0ll) + (i==0?0ll:s[i-1]);
        C[i+1] = max(res-A[i],0ll);
        res = C[i+1];
    }
    for(int i=m-1;i>=0;i--){//-1,0,+1
        for(int c=-1;c<=1;c++){
            ll gv = max(0ll,c+C[i]) + B[i];
            f[i][c+1] = min(gv,A[i]);
            if(i == m-1 && gv < A[i])
                f[i][c+1] += A[i]-gv;
            gv -= min(gv,A[i]);
            if(gv == C[i+1]-1)f[i][c+1] += f[i+1][0];
            else if(gv == C[i+1])f[i][c+1] += f[i+1][1];
            else if(gv == C[i+1]+1)f[i][c+1] += f[i+1][2];
            else assert(0);
        }
    }
    ll ans = 0;
    for(int i=1;i<m;i++)if(A[i]>0 && B[i-1]>0){
        ll val = i==1?0:s[i-2],hv = C[i-1];
        hv += B[i-1]-1;
        val += min(hv,A[i-1]);
        hv -= min(hv,A[i-1]);
        // cout<<hv<<' '<<val<<endl;
        if(i == m-1){
            val += A[i]-1;
        }else{
            hv += B[i];
            val += min(hv,A[i]-1);
            hv -= min(hv,A[i]-1);
            
            if(hv == C[i+1]-1)val += f[i+1][0];
            else if(hv == C[i+1])val += f[i+1][1];
            else if(hv == C[i+1]+1)val += f[i+1][2];
            else assert(0);
        }
        ans = max(ans, val+1);
    }
    reverse(B,B+m);
    return ans;
}
int main(){
    int Cas;
    cin>>Cas;
    while(Cas--){
        scanf("%d",&m);
        for(int i=0;i<m;i++)
            scanf("%lld",&A[i]);
        for(int i=0;i<m;i++)
            scanf("%lld",&B[i]);
        ll ans = solve();
        for(int i=0;i<m;i++)swap(A[i],B[i]);
        ans = max(ans,solve());
        printf("%lld\n",ans);
    }
    return 0;
}