#pragma GCC optimize("Ofast")

#include "bits/stdc++.h"

#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep1(i, n) for (int i = 1; i < (n); ++i)
#define rep1n(i, n) for (int i = 1; i <= (n); ++i)
#define repr(i, n) for (int i = (n) - 1; i >= 0; --i)
#define pb push_back
#define eb emplace_back
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define each(x, a) for (auto &x : a)
#define ar array
#define vec vector
#define range(i, n) rep(i, n)

using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using str = string;
using pi = pair<int, int>;
using pl = pair<ll, ll>;

using vi = vector<int>;
using vl = vector<ll>;
using vpi = vector<pair<int, int>>;
using vvi = vector<vi>;

int Bit(int mask, int b) { return (mask >> b) & 1; }

template<class T>
bool ckmin(T &a, const T &b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}

template<class T>
bool ckmax(T &a, const T &b) {
    if (b > a) {
        a = b;
        return true;
    }
    return false;
}

// [l, r)
template<typename T, typename F>
T FindFirstTrue(T l, T r, const F &predicat) {
    --l;
    while (r - l > 1) {
        T mid = l + (r - l) / 2;
        if (predicat(mid)) {
            r = mid;
        } else {
            l = mid;
        }
    }
    return r;
}


template<typename T, typename F>
T FindLastFalse(T l, T r, const F &predicat) {
    return FindFirstTrue(l, r, predicat) - 1;
}

const ll INF = 2e18;
const int INFi = 1e9;
const int N = 2e5 + 5;
const int LG = 20;

void solve() {
    int n, m;
    cin >> n >> m;
    vi a(n);
    rep(i, n) cin >> a[i];
    vi b(n);
    rep(i, n) {
        cin >> b[i];
    }
    int sz = n;
    for (int i = 1; i < n; ++i) {
        b[i] += b[i - 1];
        if (b[i] > m) {
            sz = i;
            b.resize(sz);
            break;
        }
    }
    while (sz > 0 && b[sz - 1] >= m) {
        sz--;
        b.pop_back();
    }
    while (n > 0 && a[n - 1] >= m) {
        n--;
        a.pop_back();
    }
    reverse(all(b));
    reverse(all(a));
    rep(i, n) a[i] = m - a[i];
    rep(i, sz) b[i] = m - b[i];
    int lq = 0;
    a.push_back(m);
    n++;

    ll pos = 0;
    int ans = 0;
    priority_queue<ll> have;

    rep(i, n) {
        int rq = lq;
        while (rq < sz && b[rq] <= a[i]) {
            rq++;
        }
        for (int j = lq; j + 1 < rq; ++j) {
            if (!have.empty()) {
                ll val = have.top();
                have.pop();
                ans += val;
            }
        }
        if (lq == rq) {
            have.push(a[i] - pos);
            pos = a[i];
            continue;
        }
        lq = rq;
        int j = rq - 1;
        ll val = b[j] - pos;
        if (have.empty() || val > have.top()) {
            ans += val;

            ll t = a[i] - b[j];
            if (!have.empty()) {
                t += have.top();
                have.pop();
            }
            if (t) {
                have.push(t);
            }

            pos = a[i];
            continue;
        } else {
            ll value = have.top();
            have.pop();
            ans += value;

            have.push(a[i] - pos);
            pos = a[i];
            continue;
        }
    }
    cout << ans << '\n';
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(12) << fixed;
    int t = 1;
    cin >> t;
    rep(i, t) {
        solve();
    }
    return 0;
}