#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 1000005;

int n; ll m;
int a[N]; ll b[N];

bool chk(ll x){
    int maxr = 0;
    for(int i = 1;i <= n;i ++){
        b[i] = (x + a[i] - 1) / a[i];
        if(b[i] > m) return 0;
        if(b[i] > 0) maxr = i;
    }
    if(maxr == 0) return 1;
    ll ret = 1; b[1] = max(0ll,b[1] - 1); // go to 1
    for(int i = 1;i <= maxr;i ++){
        // currently at i
        if(b[i] > 0){
            ret += 2ll * b[i];
            b[i + 1] = max(b[i + 1] - b[i],0ll);
            b[i] = 0;
        }
        if(b[i + 1] > 0 || i < maxr - 1){
            b[i + 1] = max(b[i + 1] - 1,0ll); ret ++;
        }
    }
    return ret <= m;
}

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

int main(){
    ios::sync_with_stdio(false);
    int TC;
    cin >> TC;
    while(TC --){
        solve();
    }
    return 0;
}