#include<bits/stdc++.h>
#include<ext/pb_ds/priority_queue.hpp>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define MP make_pair
#define pii pair<int,int>
const double PI=acos(-1.0);
template <class Miaowu>
inline void in(Miaowu &x){
    char c;x=0;bool f=0;
    for(c=getchar();c<'0'||c>'9';c=getchar())f|=c=='-';
    for(;c>='0'&&c<='9';c=getchar())x=(x<<1)+(x<<3)+(c^48);
    x=f?-x:x;
}
const int N=1e6+5;
int T,n;
ll m,c,a[N],b[N],d[N],use[N],id[N];
struct SGT{
    ll mn[N<<2],tag[N<<2];
    inline int ls(int u){return u<<1;}
    inline int rs(int u){return u<<1|1;}
    inline void build(int u,int l,int r){
        if(l==r)return mn[u]=d[l-1]-use[l],void();
        int mid=l+r>>1;
        build(ls(u),l,mid),build(rs(u),mid+1,r);
        mn[u]=min(mn[ls(u)],mn[rs(u)]);
    }
    inline void pd(int u){
        if(!tag[u])return;
        mn[ls(u)]+=tag[u],tag[ls(u)]+=tag[u];
        mn[rs(u)]+=tag[u],tag[rs(u)]+=tag[u];
        tag[u]=0;
    }
    inline void upd(int u,int l,int r,int L,int R,ll x){
        if(l>=L&&r<=R)return mn[u]+=x,tag[u]+=x,void();
        int mid=l+r>>1;pd(u);
        if(mid>=L)upd(ls(u),l,mid,L,R,x);
        if(mid<R)upd(rs(u),mid+1,r,L,R,x);
        mn[u]=min(mn[ls(u)],mn[rs(u)]);
    }
    inline ll qry(int u,int l,int r,int L,int R){
        if(l>=L&&r<=R)return mn[u];
        int mid=l+r>>1;pd(u);ll res=2e18;
        if(mid>=L)res=min(res,qry(ls(u),l,mid,L,R));
        if(mid<R)res=min(res,qry(rs(u),mid+1,r,L,R));
        return res;
    }
}sgt;
int main(){
    for(cin>>T;T;T--){
        in(n),in(m),in(c);d[0]=m;
        for(int i=1;i<=n;i++)in(a[i]);
        for(int i=1;i<=n;i++)in(b[i]),id[i]=i;
        for(int i=1;i<=n+1;i++)d[i]=use[i]=0;
        for(int i=1;i<=n;i++)use[i]=min(d[i-1],min(a[i]%c,b[i])),d[i]=d[i-1]+(a[i]-use[i])/c-use[i];
        sgt.build(1,1,n+1);
        for(int i=n;i>=1;i--){
            ll qwq=c*min((min(b[i],d[i-1])-use[i])/c,sgt.qry(1,1,n+1,i+1,n+1)/(c+1));
            use[i]+=qwq,sgt.upd(1,1,n+1,i,i,-qwq),sgt.upd(1,1,n+1,i+1,n+1,-qwq/c-qwq);
        }
        stable_sort(id+1,id+n+1,[](int _1,int _2){return b[_1]-use[_1]>b[_2]-use[_2];});
        priority_queue<int>Q;
        for(int ii=1,i=id[ii];ii<=n;i=id[++ii]){
            Q.push(i);
            while(!Q.empty()){
                int xx=Q.top();ll qwq=min(sgt.qry(1,1,n+1,xx,xx),sgt.qry(1,1,n+1,xx+1,n+1)-1);
                if(qwq<b[i]-use[i])break;
                qwq=min(qwq,b[xx]-use[xx]),use[xx]+=qwq;
                sgt.upd(1,1,n+1,xx,xx,-qwq),sgt.upd(1,1,n+1,xx+1,n+1,-1-qwq),Q.pop();
            }
        }
        ll ans=0;
        for(int i=1;i<=n;i++)ans+=a[i]-use[i];
        printf("%lld\n",ans);
    }
    return 0;
}