#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/hash_policy.hpp>
#define ll long long
#define all(v) v.begin(),v.end()
#define sz(v) ((int)v.size())
#define V vector
#define vi V<int>
#define vll V<ll>
#define eb emplace_back
#define pii pair<int,int>
#define pll pair<ll,ll>
#define fi first
#define se second
#define A array
#define pb push_back
#define mset multiset
#define umap __gnu_pbds::gp_hash_table
#define cerr if (test) cerr
#define freopen if (test) freopen
#define ui unsigned int
#define ull unsigned ll
#define i128 __int128
using namespace std;

const int test = 0;

namespace jhsy {
	void main() {
		ll n,m;
		cin >> n >> m;
		vll a(n);
		for (auto &x:a) {
			cin >> x;
		}
		auto calc = [&](ll x) {
			if (x == 0) {
				return 0ll;
			}
			 vll c(n),f(n),g(n);

			for (int i = 0; i < n; i++) {
				c[i] = (x+a[i]-1)/a[i];
			}
			vll p = c,q = c;
			for (int i = 0; i < n; i++) {
				p[i] = max(0ll,p[i]-1);
				if (i == 0) {
					f[i] = 1;
				}
				else {
					p[i] = max(0ll,p[i]-p[i-1]);
					f[i] = f[i-1]+2*p[i-1]+1;
				}
			}
			for (int i = n-2; i >= 0; i--) {
				ll k = max(q[i+1],1ll);
				q[i] = max(0ll,q[i]-k);
				g[i] = g[i+1]+2*k;
			}
			const ll inf = 1e18;
			ll mn = inf;
			for (int i = 0; i < n; i++) {
				ll k = 0,t = c[i]-p[i]+c[i]-q[i];
				if (t < c[i]) {
					k = 2*(c[i]-t);
				}
				mn = min(mn,f[i]+g[i]+k);
			}
			return mn;
		};
		ll l = 0,r = *ranges::min_element(a)*m+1;
		while (r-l > 1) {
			ll mid = l+((r-l)>>1);
			if (calc(mid) <= m) {
				l = mid;
			}
			else {
				r = mid;
			}
		}
		cout << l << '\n';
	}
}

int main() {
	freopen("test.in","r",stdin);
	freopen("test.out","w",stdout);
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cout << fixed << setprecision(20);

//	jhsy::init();

	int T = 1;
	cin >> T;
	while (T--) {
		jhsy::main();
	}

	return 0;
}