#include<iostream>
#include<set>
#include<bits/stdc++.h>
#define test(i) cout << #i << " "<< i << " " << endl;
using namespace std;
typedef long long ll;
inline int read()
{
    int x=0,f=1;
    char ch=getchar();
    while(ch<'0'||ch>'9')
    {
        if(ch=='-')
            f=-1;
        ch=getchar();
    }
    while(ch>='0' && ch<='9')
        x=x*10+ch-'0',ch=getchar();
    return x*f;
}
ll a[500065];
ll n, m;
bool ck(ll x)
{
    set<pair<ll, ll>>q;
    ll pd = 0;
    for (ll i = 1; i <= n; i++)
    {
        if (i <= x)
        {
            q.insert({ a[i],i });
            if (i == x)
            {
                ll u = (q.size()+1) / 2;
                auto j = q.begin();
                ll ans = 1;
                while (ans < u)
                {
                    ans++;
                    j++;
                }
                ll op = (*j).first;
                ll cnt = 0;
                for (ll k = 1; k <= x; k++)
                {
                    cnt += abs(op - a[k]);
                }
                if (cnt <= m)
                {
                    pd = 1;
                    break;
                }
            }
        }
        else
        {
            q.insert({ a[i],i });
            q.erase({ a[i - x],i - x });
            ll u = (q.size() + 1) / 2;
            auto j = q.begin();
            ll ans = 1;
            while (ans < u)
            {
                ans++;
                j++;
            }
            ll op = (*j).first;
            ll cnt = 0;
            for (ll k = i - x+1; k <= i; k++)
            {
                cnt += abs(op - a[k]);
            }
            if (cnt <= m)
            {
                pd = 1;
                break;
            }
        }
    }
    if (pd)
        return 1;
    else
        return 0;
}
signed main()
{
    ll t;
     t=read();
    while (t--)
    {
        cin >> n >> m;
        for (ll i = 1; i <= n; i++)
        {
            a[i]=read();
            a[i] -= i;
        }
        ll l = 1, r = n;
        while (l <= r)
        {
            ll mid = (l + r) >> 1;
            if (ck(mid))
            {
                l = mid + 1;
            }
            else
                r = mid - 1;
        }
        cout << r << endl;
    }

}