#include <bits/stdc++.h>

using namespace std;

#define REP(i, n) for (int i = 0; i < (n); i++)
#define REPL(i,j, n) for (int i = (j); i < (n); i++)
#define int long long
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<int,int> ii;
typedef vector<ii> vii;
const int MAXX = 1e6;

int curman[MAXX*2];

vi toclear;
int solve() {
    int n,m;cin>>n>>m;
    if (m < n) return 0;
    vi arr(n);
    REP(i, n) {
        cin>>arr[i];
    }
    int mx = 1e18;
    int mn = 1e9;
    for (auto x: arr) {
        mn = min(x, mn);
    }
    while (mn < mx) {
        int md = (mn + mx + 1)/2;
        vi farr(n);
        REP(i, n) {
            farr[i] = md/arr[i];
            if (md%arr[i] != 0) {
                farr[i]++;
            }
        }
        int needed = accumulate(farr.begin(), farr.end(), 0LL);
        int defneed = needed;
        REPL(i, 1, n) {
            int v = min(farr[i], farr[i-1]);
            farr[i-1] -= v;
            farr[i] -= v;
            if (farr[i-1] > 0) {
                needed += farr[i-1];
            }
        }
        needed += farr[n-1];
        int gg = max(defneed, needed -1);
        if (gg > m) {
            mx = md - 1;
        } else {
            mn = md;
        }
    }
    return mn;
    
}
signed main() {
    memset(curman, 0, sizeof(curman));
   ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int t; cin >> t;
    while (t--) {
        cout<<solve()<<"\n";
    }
}