#include <bits/stdc++.h>
using namespace std;
const int N = 5e5+10;
#define int long long
#define PII pair<int,int>
struct node{
    int l,r,v,cnt;
}tr[N<<2];
int n,m,a[N],mpp[N];
void pushup(int i) {
    auto &u = tr[i], &l = tr[i << 1], &r = tr[i << 1 | 1];
    u.v = l.v + r.v;
    u.cnt = l.cnt + r.cnt;
}
void build(int i,int l,int r) {
    tr[i].l = l, tr[i].r = r, tr[i].cnt = 0, tr[i].v = 0;
    if (l == r) {
        return;
    }
    int mid = l + r >> 1;
    build(i << 1, l, mid);
    build(i << 1 | 1, mid + 1, r);
}
void modify(int i,int x,int k,int k2) {
    if (tr[i].l >= x && tr[i].r <= x) {
        auto &u = tr[i];
        u.v += k;
        u.cnt += k2;
        return;
    }
    if (tr[i].l > x || tr[i].r < x)return;
    if (tr[i << 1].r >= x)modify(i << 1, x, k, k2);
    if (tr[i << 1 | 1].l <= x)modify(i << 1 | 1, x, k, k2);
    pushup(i);
}
int query(int i,int f) {
    if (tr[i].l == tr[i].r) {
        return tr[i].l;
    }
    if (tr[i << 1].cnt >= f)return query(i << 1, f);
    else return query(i << 1 | 1, f - tr[i << 1].cnt);
}
PII query(int i,int l,int r) {
    PII res = {0, 0};
    if (tr[i].l >= l && tr[i].r <= r) {
        auto &u = tr[i];
        return {u.v, u.cnt};
    }
    if (tr[i].l > r || tr[i].r < l)return res;
    if (tr[i << 1].r >= l) {
        PII now = query(i << 1, l, r);
        res.first += now.first;
        res.second += now.second;
    }
    if (tr[i << 1 | 1].l <= r) {
        PII now = query(i << 1 | 1, l, r);
        res.first += now.first;
        res.second += now.second;
    }
    return res;
}
void solve() {
    cin >> n >> m;
    map<int, int> mp;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
        a[i] -= i;
        mp[a[i]]++;
    }
    int idx = 0;
    for (auto[pos, w]: mp) {
        ++idx;
        mp[pos] = idx;
        mpp[idx] = pos;
    }
    int ans = 1;
    build(1, 1, n);
    for (int i = 1, j = i; i <= n && j <= n; i++) {
        while (j <= n) {
            modify(1, mp[a[j]], a[j], 1);
            int mid = j - i + 1;
            int z = mpp[query(1, (mid + 1) / 2)];
            auto[lv, lcnt]=query(1, 1, mp[z]);
            auto[rv, rcnt]=query(1, mp[z] + 1, idx);
            if (lcnt * z - lv + rv - rcnt * z <= m) {
                ans = max(ans, mid);
                j++;
            } else {
                modify(1, mp[a[i]], -a[i], -1);
                modify(1, mp[a[j]], -a[j], -1);
                break;
            }
        }
    }
    cout << ans << '\n';
}
signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int t;cin >> t;
    while (t--) {
        solve();
    }
}