//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],c[N],cs[N];

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

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

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

    // 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;
}