#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N=1e6+5;
const ll I=1e18;
int t,n,a[N],b[N];
ll ans,x,y,z;
namespace IO
{
    const int S=(1<<20);
    char in[S],out[S],*p1=in,*p2=in,*p3=out;
    char gc() {return p1==p2&&(p2=(p1=in)+fread(in,1,S,stdin),p1==p2)?EOF:*p1++;}
    void flush() {fwrite(out,1,p3-out,stdout);p3=out;}
    void pc(char c)
    {
        if(p3==out+S) flush();
        *p3++=c;
    }
    template<class T>void read(T &x)
    {
        x=0;int t=0;char c=gc();
        for(;!isdigit(c);c=gc()) if(c=='-') t=1;
        for(;isdigit(c);c=gc()) x=(x<<1)+(x<<3)+(c^48);
        if(t) x=-x;
    }
    template<class T>void write(T x,char c='\n')
    {
        if(x<0) pc('-'),x=-x;
        static int s[40],top=0;
        do s[++top]=x%10,x/=10;while(x);
        while(top) pc(s[top--]+48);
        pc(c);
    }
    struct F {~F(){flush();};}f;
}
using IO::read;
using IO::write;
void solve()
{
    read(n);ans=0;x=y=z=0;
    for(int i=1;i<=n;i++) read(a[i]);
    for(int i=1;i<=n;i++) read(b[i]);
    for(int i=1;i<=n;i++)
    {
        if(b[i]==0)
        {
            if(x<a[i])
            {
                ll v=min(z,a[i]-x);
                x+=v,y+=v,z-=v;ans+=v;
                if(x<a[i]) ans+=(a[i]-x),x=a[i];
            }
        }
        else
        {
            if(a[i]==0) return write(-1),void();
            if(a[i]-b[i]<=x&&b[i]-a[i]>y)
            {
                ll v=min(z,b[i]-a[i]-y);
                ans+=v,x+=v,y+=v,z-=v;
            }
            if(b[i]-a[i]<=y&&a[i]-b[i]>x)
            {
                ll v=min(z,a[i]-b[i]-x);
                ans+=v,x+=v,y+=v,z-=v;
            }
            x=min(x,(ll)a[i]-1);y=min(y,(ll)b[i]-1);
            if(a[i]-b[i]<=x&&b[i]-a[i]<=y)
            {
                if(x+b[i]-y-a[i]>=0) z=min({z,a[i]-1-x,b[i]-1-y})+(x+b[i]-y-a[i]),x=y+a[i]-b[i];
                else z=min({z,a[i]-1-x,b[i]-1-y})+(y+a[i]-x-b[i]),y=x+b[i]-a[i];
                continue;
            }
            if(a[i]-b[i]<=x)
            {
                ans+=(b[i]-a[i]-y);
                z=x;x=0;y=b[i]-a[i];
                continue;
            }
            if(b[i]-a[i]<=y)
            {
                ans+=(a[i]-b[i]-x);
                z=y;y=0;x=a[i]-b[i];
                continue;
            }
        }
    }
    write(ans);
}
int main()
{
    read(t);
    while(t--) solve();
    return 0;
}