#include <bits/stdc++.h>

using ll = long long;
using namespace std;

const int MAXN = 200'001;

struct Node {
    Node *nxt[2];
    int siz;

    Node() {
        nxt[0] = nxt[1] = nullptr;
        siz = 0;
    }
};

void add(Node *root, ll val) {
    root->siz++;
    for (int i = 60; i >= 0; i--) {
        int bit = (val >> i) & 1;
        if (!root->nxt[bit]) root->nxt[bit] = new Node();
        root = root->nxt[bit];
        root->siz++;
    }
}

void solve() {
    ll n, k; cin >> n >> k;
    Node *root = new Node();    
    vector<ll> a(n + 1);
    for(int i = 1; i <= n; i++) cin >> a[i];
    vector<Node *> pt(n + 1, root);
    for(int i = 1; i <= n; i++) 
    {
        ll x;
        cin >> x;
        add(root, x);
    }
    ll ans = 0;
    for(int j = 60; j >= 0; j--)
    {
        ll x = 0;
        for(int i = 1; i <= n; i++) {
            if(pt[i] && pt[i]->nxt[(a[i] >> j) & 1]) x += pt[i]->nxt[(a[i] >> j) & 1]->siz;
        }
        if(x < k)
        {
            ans |= 1LL<<j;
            k -= x;
            for(int i = 1; i <= n; i++)
            {
                if (!pt[i]) continue;
                int dir = !((a[i] >> j) & 1);
                if(!pt[i]->nxt[dir]) pt[i] = nullptr;
                else pt[i] = pt[i]->nxt[dir];
            }
        } else {
            for (int i = 1; i <= n; i++) {
                if (!pt[i]) continue;
                int dir = (a[i] >> j) & 1;
                if(!pt[i]->nxt[dir]) pt[i] = nullptr;
                else pt[i] = pt[i]->nxt[dir];
            }
        }
    }
    cout << ans << "\n";
}

int main() {
    ios_base::sync_with_stdio(0); cin.tie(0);
    int t = 1;
    cin >> t;
    while (t--) {
        solve();
    }
    return 0;
}