#include <iostream>
#include <string>
#include <string.h>
#include <vector>
#include <algorithm>
#include <cmath>
#include <set>
#include <random>
#include <cstdlib>
#include <numeric>
#include <functional>
#include <queue>
using namespace std;
using ll = long long;
ll mod = 1e9 + 7;

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

	vector<ll> data(n + 1);
	vector<ll> tim(n + 2);
	for (int i = 1; i <= n; i++) cin >> data[i];
	
	ll mi = data[0];

	for (int i = 1; i <= n; i++) {
		if (data[i] == 0) {
			cout << 0 << endl;
			return;
		}
		mi = min(data[i], mi);
	}
	ll l = 0, r = (ll)mi * m;
	function<ll(ll)> check = [&](ll low) {
		if (low == 0) return 0LL;

		for (int i = 1; i <= n; i++) tim[i] = (low + data[i] - 1) / data[i];
		
		ll ned = 0;
		
		for (int i = 1; i <= n; i++) {
            // 第一次走过来
			ned++;
			tim[i]--;

			// 如果小于0可以直接走到下一个点
			if (tim[i] <= 0) continue;
			
	
			ll tmp = min(tim[i], tim[i + 1]);
			ned += tmp * 2LL;
	
			tim[i] -= tmp;
			tim[i + 1] -= tmp;

			ned += tim[i] * 2LL;

			// 如果最后一个数已经达标,不必要走
			if (i + 1 == n && tim[i + 1] <= 0) break;
		}

		return ned;
	};

	while (l < r) {
		ll mid = (l + r) / 2LL + 1LL;

		if (check(mid) > m) 
			r = mid - 1;
		else 
			l = mid;
	}

	cout << l << endl;
	
}

int main()
{
	//freopen("out.txt", "w", stdout);
	//freopen("in.txt", "r", stdin);
	ios::sync_with_stdio(false);

	cin.tie(0);
	cout.tie(0);

	int cnt = 1;
	cin >> cnt;

	while (cnt--)
	{
		slove();
	}
};