#include<bits/stdc++.h>
using namespace std;
using ll = long long;
void solve() {
	int n, m, mx = 0;
	cin >> n >> m;
	std::vector<int> a(n + 1);
	for(int i = 1; i <= n; i++) {
		cin >> a[i];
		mx = max(mx, a[i]);
	}
	ll L = 0, R = m * mx, ans = 0;
	while(L <= R) {
		ll mid = L + R >> 1;
		int cnt = 0;
		std::vector<int> vis(n + 1, 0);
		for(int i = 1; i < n; i++) {
			if(ceil(1.0 * mid / (1.0 * a[i])) > vis[i]) 
				cnt += 2 * (ceil(1.0 * mid / (1.0 * a[i])) - vis[i]) - 1;
			vis[i + 1] += ceil(1.0 * mid / (1.0 * a[i])) - 1;
		}
		if(vis[n] < ceil(1.0 * mid / (1.0 * a[n]))) 
			cnt += 2 * (ceil(1.0 * mid / (1.0 * a[n])) - vis[n]) - 1;
		if(cnt <= m) ans = mid, L = mid + 1;
		else R = mid - 1;
	}
	cout << ans << '\n';
	return;
}
int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0), cout.tie(0);
	int t = 1;
	cin >> t;
	while(t--) solve();
	return 0;
}