#include <bits/stdc++.h>

using namespace std;

int T;
 using ll =long long ;
#define int ll
 void solve(){
     int n,m;
     cin>>n>>m;
     vector<int> v1(n+3),v2(n+3);
     for(int i =1;i<=n;i++){
         cin>>v1[i];
     }
     int l = 0;
     int r = 1e18+3;
     auto  checked=[&](int mid)->bool {

         for(int i=1;i<=n;i++){
//             v2[i]= mid/v1[i];
             v2[i]= (v1[i]+mid -1)/v1[i];
         }
         int sums=0;
         for(int i=1;i<=n;i++){
             if(v2[i]<=0 && i != n) {
                 sums++;
                 continue;
             }
             sums++;
             v2[i]--;
             sums+=2*v2[i];
             v2[i+1]-=v2[i];
//             sums+=2*v2[i];
//             v2[i+1]-=v2[i];
         }


         return sums<=m;
     };


     while (l<r){
         int mid = (l+r+1)/2;
         if(checked(mid)){
             l= mid;
         }else {
             r= mid -1;
         }
     }
   //  checked(5);
     cout<<l<<endl;
 }

#undef int


int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cin >> T;
    while (T--) {
        solve();
    }
}