#include<bits/stdc++.h>
#define int long long

using namespace std;

const int N = 2e5 + 7;
int a[N];
int n,m;

bool check(int x){
	int cnt = 0;
	int sum = 0;
	vector<int> v(n + 1,0);
	for(int i = 1;i <= n;i ++){
		if(v[i] >= x){
			sum ++;
			continue;
		} else{
			int rd = x - v[i];
			rd = (rd + a[i] - 1) / a[i];
			sum += 2 * rd - 1;
			if(sum > m) return false;
			v[i + 1] += (rd - 1) * a[i + 1];
		}
	} return true;
}

void solve(){
	cin >> n >> m;
	for(int i = 1;i <= n;i ++) cin >> a[i];
	int l = 0,r = 1e18;
	while(l < r){
		int mid = l + r + 1 >> 1;
		if(check(mid)){
			l = mid; 
		} else{
			r = mid - 1;
		}
	} cout << l << endl;
}

signed main(){
	ios::sync_with_stdio(false);
	cin.tie(nullptr),cout.tie(nullptr);
	int t; cin >> t;
	while(t --){
		solve();
	} return 0;
}