Untitled

#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    
    int t;
    cin >> t;
    while (t--) {
        int n;
        int k;
        cin >> n >> k;
        vector<int> a(n), b(n);
        for (auto &x : a) cin >> x;
        for (auto &x : b) cin >> x;

        set<int> options(a.begin(), a.end());
        options.insert(b.begin(), b.end());

        sort(a.begin(), a.end());
        sort(b.begin(), b.end());

        int answer = 0;
        for (int x : options) {
            int A = n - (lower_bound(a.begin(), a.end(), x) - a.begin());
            int B = n - (lower_bound(b.begin(), b.end(), x) - b.begin());

            if (B - A <= k) {
                answer = max(answer, x * B);
            }
        }

        cout << answer << "\n";
    }
}