#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 + 2, 0);
		for(int i = 1; i <= n; i++) {
			int now = mid / a[i] + (mid % a[i] != 0);
			if(now > vis[i]) 
				cnt += 2 * (now - vis[i]) - 1;
			else cnt ++;
			vis[i + 1] += now - 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;
}