#include <bits/stdc++.h>
//#include <bits/extc++.h>
//using namespace __gnu_pbds;
using namespace std;
#define int long long int
 
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define repb(i, a, b) for(int i = (a); i >= (b); --i)
#define trav(a, x) for(auto& a : x)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define ff first
#define ss second
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef vector<int> vi;
#define pb push_back
 
#define ln '\n'
template<typename T1,typename T2>
ostream& operator <<(ostream& c,pair<T1,T2> &v){
	c<<"("<<v.ff<<","<<v.ss<<")"; return c;
}
template <template <class...> class TT, class ...T>
ostream& operator<<(ostream& out,TT<T...>& c){
    out<<"{ ";
    for(auto &x : c) out<<x<<" ";
    out<<"}"; return out;
}
 
const int MOD = 1e9+7, LIM = 2e5+5;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
 
int n, m;
int a[LIM];
 
bool attain(int v){
 
	int b[n];
	rep(i, 0, n) {
		b[i] = (v + a[i]-1)/a[i];
		b[i]--;
	}
	//init it
	int best = n;
	rep(i, 1, n) {
		best += 2*max(0LL, b[i-1]);
		b[i] -= max(0LL, b[i-1]);
	}
	if (b[n-1] <= -1) best--;
	best += 2*max(0LL, b[n-1]);
	// cerr << ?best << " " << v << ln;
	return (best<=m);
}
 
signed main() {
	cin.tie(0)->sync_with_stdio(0);
	cin.exceptions(cin.failbit);
 
	int tests = 1;
	cin >> tests;
 
	while(tests--){
		cin >> n >> m;
		rep(i, 0, n) cin >> a[i];
		int l = 0, r = 100000 * m + 1;
		while(l < r){
			// find last val which attainable
			int mid = (l+r)/2;
			if(attain(mid)){
				l = mid+1;
			}		
			else{
				r = mid;
			}
		}
		cout << l-1 << endl;
	}
	return 0;
}