Untitled

#include <bits/stdc++.h>
using namespace std;
//codewithabby
int main() {
    int t;
    cin >> t;
    while (t--) {
        int n, k;
        cin >> n >> k;
        vector<long long> a(n);
        for (int i = 0; i < n; i++) {
            cin >> a[i];
        }
        long long left = 1, right = 1e14, ans = 0;
        while (left <= right) {
            long long mid = (left + right) / 2;
            long long cnt = 0;
            for (int i = 0; i < n; i++) {
                cnt += (mid / (a[i] * (i + 1)));
            }
            if (cnt >= k) {
                ans = mid;
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }
        cout << ans << endl;
    }
    return 0;
}