#include <bits/stdc++.h>
#define int long long
using namespace std;
inline int read(){
    int x=0,f=1;char ch=getchar();
    for(;!isdigit(ch);ch=getchar())f^=ch=='-';
    for(;isdigit(ch);ch=getchar())x=x*10+(ch^48);
    return f?x:-x;
}
inline void chmin(int &x,int y){x=min(x,y);}
inline void chmax(int &x,int y){x=max(x,y);}
const int N=5e5+5,inf=1e15;
int n,sa,sb,A[N],B[N],oriA[N],oriB[N];
void solve(){
    n=read();
    for(int i=0;i<n;++i)sa+=(A[i]=read());
    for(int i=0;i<n;++i)sb+=(B[i]=read());
    if(sa<sb)A[0]+=sb-sa;
    else B[0]+=sa-sb;
    memcpy(oriA,A,sizeof(A));
    memcpy(oriB,B,sizeof(B));
    int cnt=0,tag=0;
    for(int i=0,j=n-1;i<n;++i){
        while(A[i]>0&&j>=0&&i+j>=n-1){
            if(!B[j])--j;
            else{
                int delta=min(A[i],B[j]);
                A[i]-=delta;
                B[j]-=delta;
                cnt+=delta;
                if(i+j>=n)tag=1;
            }
        }
    }
    if(tag){
        printf("%lld\n",cnt);
        return;
    }
    int up=-inf,down=inf;
    for(int i=0;i<n;++i){
        if(A[i])chmax(up,i);
        if(oriA[i]>A[i])chmin(down,i);
    }
    if(down<up)tag=1;
    up=-inf,down=inf;
    for(int i=0;i<n;++i){
        if(B[i])chmax(up,i);
        if(oriB[i]>B[i])chmin(down,i);
    }
    if(down<up)tag=1;
    if(!tag)--cnt;
    int FIND=-1;
    for(int i=n-1;i>=0;--i)if(oriA[i]){
        for(int j=n-1;j>=0;--j)if(oriB[j]){
            FIND=i+j;
            break;
        }
        if(FIND!=-1)break;
    }
    if(FIND<n){
        puts("0");
        return;
    }
    printf("%lld\n",cnt);
}
signed main(){
    // freopen("test.out","w",stdout);
    for(int cas=read();cas--;)solve();
}