#define _CRT_SECURE_NO_WARNINGS 1
#include<bits/stdc++.h>
#include<unordered_map>
#include<unordered_set>
using namespace std;
#define ll long long
//#define double long double
#define lc u<<1
#define rc u<<1|1
#define X first
#define Y second
#define endl "\n"
#define int long long
const int N = 2e3 + 50;
const int M = 5e5 + 5;
const ll maxm = 1e18 + 5;
const ll mod = 998244353;
int dx[] = { -1,0,1,0 };
int dy[] = { 0,1,0,-1 };
//random_shuffle(id + 1, id + n + 1);
ll ksm(ll a, ll b);
ll gcd(ll a, ll b);

template<class T>inline void read(T& x) {
	x = 0;
	char c = getchar();
	while (!isdigit(c))c = getchar();
	while (isdigit(c))x = x * 10 + (c & 15), c = getchar();
}

void write(ll x)
{
	if (x < 0)
		putchar('-'), x = -x;
	if (x > 9)
		write(x / 10);
	putchar(x % 10 + '0');
	return;
}

ll n, m;
ll a[N];
ll va[N];

bool check(ll val) {
	//至少要达到value
	for (int i = 1; i <= n; i++)va[i] = 0;
	ll mid = m;
	for (int i = 1; i <= n; i++) {
		if (mid == 0) {//先判断能否到这一步
			if (va[n] >= val)return true;
			return false;
		}
		mid--; va[i] += a[i];
		if (mid == 0) {//先判断能否到这一步
			if (va[n] >= val)return true;
			return false;
		}
		if (va[i] >= val)continue;
		ll dis = val - va[i];
		ll cnt = dis / a[i];
		if (dis % a[i] != 0)cnt++;
		if (mid < cnt * 2)return false;
		mid -= (cnt * 2); va[i + 1] += a[i + 1] * cnt;
		if (mid == 0) {
			if (va[n] >= val)return true;
			return false;
		}
	}
	return true;
}

void solve()
{
	//这我之前好像补过，lyr给调出来了，在gym交了，再写一发
	cin >> n >> m;
	for (int i = 1; i <= n; i++)cin >> a[i];
	if (m < n) {
		cout << 0 << endl;
		return;
	}
	ll l = 0, r = maxm;
	while (l + 1 < r) {
		ll mid = (l + r) >> 1;
		if (check(mid)) {//合法让l过去
			l = mid;
		}
		else r = mid;
	}
	cout << l << endl;
	return;
}


signed main()
{
	ios::sync_with_stdio(false);
	cin.tie(0), cout.tie(0);
	int T = 1;
	cin >> T;
	//read(T);
	while (T--)
		solve();
	return 0;
}

/*PonyHex*/


ll ksm(ll a, ll b) {
	ll base = a;
	ll ans = 1;
	while (b) {
		if (b & 1)ans *= base % mod;
		ans %= mod;
		base *= base; base %= mod;
		b >>= 1;
	}
	return ans % mod;
}
ll gcd(ll a, ll b) {
	return b ? gcd(b, a % b) : a;
}