//And He found you lost and guided [you] [93:07]

//#pragma GCC optimize ("Ofast")
//#pragma GCC target ("avx2")
//#pragma GCC optimize("unroll-loops")

#include<bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> pll;
typedef pair<int,int> pii;
typedef vector<ll> vll;
typedef vector<int> vii;
typedef map<int,int> mpi;
typedef map<ll,ll> mpl;
typedef unordered_map<int,int> umpi;
typedef unordered_map<ll,ll> umpl;

#define modu 998244353 
#define mod 1000000007
#define eps 1e-9
#define inf 1000000000000000006
#define ff first
#define ss second
#define pb push_back
#define all(v) v.begin(), v.end()
#define fastio ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
#define endl '\n'
// #define pi acos(-1.0)
#define dec(n) fixed << setprecision(n)
#define N 300005
#define int long long

int n,m,a[N];;

int chk(int x){
    int moves=0;
    vector<int> c(n+3,0);

    if(x==0) return 1;
    
    for(int i=1;i<=n;i++){
        c[i]+=(x+a[i]-1)/a[i];
        if(i==n && c[i]<=0) moves--;
        c[i]=max(1LL,c[i]);
        moves+=(c[i]*2)-1;
        c[i+1]-=(c[i]-1);

        if(moves>m) return 0;
        
        // cout << moves << " ";

    }
    
    // cout << moves << " ";
    return moves<=m;
}

void solve(){
    cin >> n >> m;
    for(int i=1;i<=n;i++) cin >> a[i];

    // cout << chk(4) << endl;
    // for(int i=0;i<=10;i++) cout << i << "  ->  " << chk(i) << endl;

    int lo=0,hi=1e18,ans;
    while(lo<=hi){
        int mid=(lo+hi)/2;
        if(chk(mid)){
            ans=mid;
            lo=mid+1;
        }
        else hi=mid-1;
    }

    
    cout << ans << endl;

    




    





}


signed main(){
    fastio;
    //srand(chrono::steady_clqk::now().time_since_epqh().count());
    // fflush(stdout);
    int T=1,cs=0;
    cin >> T;
    while(T--){
        //cout << "Case " << ++cs << ": " ; 
        solve();
    } 
    return 0;
}