#include <bits/stdc++.h>
#define fi first
#define se second
#define pb push_back
using namespace std;

using ll = long long;
const ll N = 1000010, inf = 3e15, SZ = (1 << 18) + 5;
static char buf[SZ], *bgn = buf, *til = buf;
char getc() {
    if(bgn == til)  bgn = buf, til = buf + fread(buf, 1, SZ, stdin);
    return bgn == til ? EOF : *bgn++;
}
template<typename T>
void read(T &x) {
    char ch = getc();  T fh = 0;   x = 0;
    while(ch < '0' || ch > '9')    fh |= (ch == '-'), ch = getc();
    while(ch >= '0' && ch <= '9')   x = x * 10 + ch - '0', ch = getc();
    x = fh ? -x : x;
}
template<typename Type, typename... argc>
void read(Type &x, argc &...args)   {read(x), read(args...);}
template<typename T>
void print(T x) {
    if(x < 0)  putchar('-'), x = -x;
    if(x / 10)  print(x / 10);
    putchar(x % 10 + '0');
}
// 好牛的贪心啊，最后一部分感性理解每次取大的很优，但感觉严谨证明有点困难啊......
int n, m, cnt;
ll s[N], x[N], a[N], b[N], res[N], lsh[N], c, ans;
vector<int> upd[N];
struct segtree {
    ll mn[N << 2], tag[N << 2];
    int ls(int x)   {return x << 1;}
    int rs(int x)   {return x << 1 | 1;}
    void pushup(int x)  {mn[x] = min(mn[ls(x)], mn[rs(x)]);}
    void upd(int x, ll val) {mn[x] += val, tag[x] += val;}
    void pushdown(int x)    {if(tag[x] != 0)    upd(ls(x), tag[x]), upd(rs(x), tag[x]), tag[x] = 0;}
    void build(int l, int r, int p) {
        tag[p] = 0;
        if(l == r)  return void(mn[p] = res[l]);
        int mid = (l + r) >> 1;
        build(l, mid, ls(p)), build(mid + 1, r, rs(p)), pushup(p);
    }
    void update(int l, int r, ll val, int nl = 1, int nr = n, int p = 1) {
        if(l > r)   return;
        if(l <= nl && nr <= r)  return upd(p, val);
        int mid = (nl + nr) >> 1;   pushdown(p);
        if(mid >= l)    update(l, r, val, nl, mid, ls(p));
        if(mid < r) update(l, r, val, mid + 1, nr, rs(p));
        pushup(p);
    }
    ll query(int l, int r, int nl = 1, int nr = n, int p = 1) {
        if(l > r)   return inf;
        if(l <= nl && nr <= r)  return mn[p];
        int mid = (nl + nr) >> 1;   ll res = inf;   pushdown(p);
        if(mid >= l)    res = min(res, query(l, r, nl, mid, ls(p)));
        if(mid < r) res = min(res, query(l, r, mid + 1, nr, rs(p)));
        return res;
    }
}tree;
void mian() {
    read(n, m, c), s[0] = m, cnt = ans = 0;
    for(int i = 1; i <= n; ++i) read(a[i]), x[i] = 0, upd[i].clear();
    for(int i = 1; i <= n; ++i) read(b[i]);
    for(int i = 1; i <= n; ++i) {
        x[i] = min({a[i] % c, s[i - 1], b[i]});
        s[i] = s[i - 1] + (a[i] - x[i]) / c - x[i];
    }
    ll tmp = inf; // min_{j=i}^n s_j - x_{j+1}
    for(int i = n; i > 0; --i) {
        ll num = min({(b[i] - x[i]) / c, (s[i - 1] - x[i]) / c, tmp / (c + 1)}); 
        x[i] += num * c, tmp = min(tmp - num * (c + 1), s[i - 1] - x[i]); // j\in [i, n] s_j \gets s_j - num * (c + 1)
    }
    for(int i = 1; i <= n; ++i) s[i] = s[i - 1] + (a[i] - x[i]) / c - x[i], res[i] = s[i - 1] - x[i], lsh[++cnt] = b[i] - x[i];
    sort(lsh + 1, lsh + cnt + 1), cnt = unique(lsh + 1, lsh + cnt + 1) - (lsh + 1), reverse(lsh + 1, lsh + cnt + 1);
    tree.build(1, n, 1), lsh[cnt + 1] = 0;
    for(int i = 1; i <= n; ++i) {
        int p = lower_bound(lsh + 1, lsh + cnt + 1, b[i] - x[i], greater<ll>()) - lsh;
        upd[p].pb(i);
        // assert(res[i] >= 0), assert(b[i] >= x[i]);
    }
    priority_queue<int> heap; // \forall j < i, d_j \le d_i
    for(int i = 1; i <= cnt; ++i) {
        for(int x : upd[i]) heap.push(x);
        while(!heap.empty()) {
            int x = heap.top(); 
            ll d = min(tree.query(x, x), tree.query(x + 1, n) - 1); // d_i = min(res_i, min_{j>i} res_j - 1)
            if(d <= lsh[i + 1])   break;
            heap.pop();
            ll num = min({d, lsh[i], c - 1});
            ::x[x] += num, tree.update(x + 1, n, -num - 1), tree.update(x, x, -num);
        }
    }   
    for(int i = 1; i <= n; ++i) ans += a[i] - x[i];
    print(ans), putchar('\n');
}
int main() {
    #ifdef Kelly
        freopen("in.txt", "r", stdin);
        freopen("out.txt", "w", stdout);
        freopen("err.txt", "w", stderr);
    #endif
    int T = 1;  read(T);
    while(T--)  mian();
    return 0;
}