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

typedef long long LL;
typedef pair<int,int> P;
const LL mod=998244353;
const int INF=0x3f3f3f3f;
const int N=1e5+10;
LL a[N],b[N];
LL n,m;

int check(LL x)
{
    for(int i=1;i<=n;i++) b[i]=(x+a[i]-1)/a[i];
    
    LL cnt=0;
    LL last=0;
    
    for(int i=1;i<=n;i++)
    {
        if(b[i]>0) last=i;
        
        cnt++;
        b[i]--;
        
        if(b[i]>0)
        {
            cnt+=b[i]*2;
            b[i+1]-=(b[i]-1);
        }
    }
    
    cnt-=(n-last);
    
    if(cnt<=m) return 1;
    return 0;
    
}

void solve()
{
    cin>>n>>m;
    
    for(int i=1;i<=n;i++) cin>>a[i];
    
    LL l=0,r=1e17;
    
    while(l<r)
    {
        LL mid=(l+r+1)/2;
        
        if(check(mid)) l=mid;
        else r=mid-1;
    }
    
    cout<<l<<endl;
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    
    int tt; cin>>tt;
    
    while(tt--) solve();
    
    return 0;
}