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

#define forn(i,a,b) for(int i = a; i < (b); i++)
#define fore(i,a,b) for(int i = a; i <= (b); i++)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()

using ll = long long;
using ld = long double;
using ii = pair<int, int>;

void water_ij_until_i_near_target(ll target, const vector<ll> &a, vector<ll> &d, size_t i, size_t j, ll &m) {
    if (d[i] >= target) return;
    ll waters = (target - d[i] - 1) / a[i];
    if (waters == 0) return;
    // cout << "watered " << i << " and " << j << ", took " << (waters * 2) << " waters" << endl;
    d[i] += waters * a[i];
    d[j] += waters * a[j];
    m -= 2 * waters;
}

bool canReach(ll target, const vector<ll> &a, ll n, ll m) {
    // cout << "target: " << target << endl;

    vector<ll> d = a;
    m -= n;

    forn(i, 0, n - 1) {
        water_ij_until_i_near_target(target, a, d, i, i+1, m);
        if (m < 0) return false;
    }

    water_ij_until_i_near_target(target, a, d, n - 1, n - 2, m);

    int cur_run = 0;
    forn(i, 0, n) {
        if (d[i] < target) {
            cur_run++;
        } else if (cur_run) {
            ll waters = 0;
            if (i == n - 1) {
                waters = cur_run;
            } else {
                waters = (cur_run + 1) / 2 * 2;
            }
            m -= waters;
            // cout << "run from " << (i - cur_run) << " to " << (i - 1) << " took " << waters << endl;
            cur_run = 0;
        }
    }

    if (cur_run != 0) {
        ll waters = (cur_run + 1) / 2 * 2;
        // cout << "final run from " << (n - cur_run) << " to " << (n - 1) << " took " << waters << endl;
        m -= waters;
    }
    // if (m >= 0) cout << "success" << endl;
    return m >= 0;
}

void solve()
{
    ll n, m;
    cin >> n >> m;

    if (m < n) {
        cout << 0 << endl;
        return;
    }

    vector<ll> a(n, 0);
    forn(i,0,n) cin >> a[i];

    ll left = 0;
    ll right = (*max_element(all(a)) + n - 1) / n * m;
    // cout << "right "<<right <<endl;
    while (left < right) {
        ll mid = left + (right - left + 1) / 2;
        if (canReach(mid, a, n, m)) {
            left = mid;
        } else {
            right = mid - 1;
        }
    }
    cout << right << endl;
}

int main()
{
    cin.tie(0)->sync_with_stdio(0);

    int t; cin>>t;
    forn(i,0,t) solve();
}