#include <bits/stdc++.h>
using namespace std;

using i64 = long long;

struct Fenwick {
    int n;
    vector<i64> f;
    vector<int> f1;

    Fenwick() {}
    Fenwick(int n) {
        init(n);
    }

    void init(int n) {
        this->n = n;
        f.assign(n + 1, 0);
        f1.assign(n + 1, 0);
    }

    void add(int x, i64 y, int flag) {
        if (flag == 1) {
            while (x <= n) {
                f[x] += y;
                f1[x]++;
                x += x & -x;
            }
        } else {
            while (x <= n) {
                f[x] -= y;
                f1[x]--;
                x += x & -x;
            }
        }
    }

    pair<i64, int> sum(int x) {
        i64 ret = 0;
        int r1 = 0;
        while (x > 0) {
            ret += f[x];
            r1 += f1[x];
            x -= x & -x;
        }
        return make_pair(ret, r1);
    }
};

void solve() {
    int n;
    i64 m;
    cin >> n >> m;

    vector<i64> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
        a[i] += (n - i - 1);
    }

    // for (int i = 0; i < n; i++) {
    //     cerr << a[i] << " \n"[i == n - 1];
    // }
    // cerr << "---" << endl;

    vector<i64> pre(n + 1, 0);
    for (int i = 0; i < n; i++) {
        pre[i + 1] = pre[i] + a[i];
    }

    auto check = [&](int x) -> bool {
        // cerr << x << endl;

        vector<i64> v = a;
        for (int i = x; i <= n; i++) {
            v.push_back((pre[i] - pre[i - x]) / x);
            v.push_back((pre[i] - pre[i - x]) / x + 1);
        }

        sort(v.begin(), v.end());
        v.erase(unique(v.begin(), v.end()), v.end());

        // for (int i = 0; i < v.size(); i++) {
        //     cerr << v[i] << " \n"[i == v.size() - 1];
        // }

        int N = v.size();
        Fenwick f(N);

        for (int i = 0; i < x - 1; i++) {
            f.add(lower_bound(v.begin(), v.end(), a[i]) - v.begin() + 1, a[i], 1);
        }

        bool ret = 0;
        for (int i = x - 1; i < n; i++) {
            f.add(lower_bound(v.begin(), v.end(), a[i]) - v.begin() + 1, a[i], 1);

            i64 cal = pre[i + 1] - pre[i + 1 - x];
            i64 c1 = cal / x, c2 = c1 + 1;

            auto [s1, n1] = f.sum(lower_bound(v.begin(), v.end(), c1) - v.begin() + 1);
            auto [s2, n2] = f.sum(lower_bound(v.begin(), v.end(), c2) - v.begin() + 1);

            i64 need1 = (1LL * n1 * c1 - s1 + (cal - s1) - (1LL * (x - n1) * c1));
            i64 need2 = (1LL * n2 * c2 - s2 + (cal - s2) - (1LL * (x - n2) * c2));

            // cerr << "i: " << i + 1 << ", need1: " << need1 << ", need2: " << need2 << endl;
            // cerr << "c1: " << c1 << ", c2: " << c2 << endl;
            // cerr << "sum1: " << s1 << ", n1: " << n1 << endl;
            // cerr << "sum2: " << s2 << ", n2: " << n2 << endl;

            if (need1 <= m || need2 <= m) {
                ret = 1;
                break;
            }

            f.add(lower_bound(v.begin(), v.end(), a[i - x + 1]) - v.begin() + 1, a[i - x + 1], 0);
        }

        return ret;
    };

    int lo = 1, hi = n;
    while (lo < hi) {
        int mid = (lo + hi + 1) >> 1;
        if (check(mid)) {
            lo = mid;
        } else {
            hi = mid - 1;
        }

        // cerr << "---" << endl;
    }

    cout << lo << endl;
}

int main(void)
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int t;
    cin >> t;

    while (t--) {
        solve();
    }

    return 0;
}