[CSES] Apartments

void solve() {
    ll n, m, k;
    cin >> n >> m >> k;

    vll a(n);
    multiset<ll> b;

    rep(i, n) cin >> a[i];
    sort(all(a));

    rep(i, m) {
        ll x;
        cin >> x;
        b.insert(x);
    }

    ll ans = 0;
    rep(i, n) {
        ll x = a[i] - k;
        auto it = b.lower_bound(x);
        if (it != b.end()) {
            if (*it <= a[i] + k) {
                ans++;
                b.erase(it);
            }
        }
    }

    cout << ans << "\n";
}