#include <bits/stdc++.h>
using namespace std;

struct iofast_t {
    iofast_t() {
        ios::sync_with_stdio(false);
        cin.tie(nullptr);
    }
} iofast;

struct uns_t {} uns;
template <typename Element, typename Head, typename ...Args>
auto vec(Element init, Head arg, Args ...args) {
    if constexpr (sizeof...(Args) == 0) return vector(arg, init);
    else return vector(arg, vec(init, args...));
}
template <typename Element, typename Head, typename ...Args>
auto vec(uns_t, Head arg, Args ...args) {
    return vec(Element(), arg, args...);
}

template <typename Container>
auto distance(const Container &c, decltype(begin(c)) iter) {
    return distance(begin(c), iter);
}

template <typename RIter, typename Compare = less<typename iterator_traits<RIter>::value_type>>
auto isort(RIter first, RIter last, Compare comp = Compare()) {
    vector<int> i(distance(first, last));
    iota(begin(i), end(i), 0);
    sort(begin(i), end(i), [&](auto x, auto y) {
        return comp(*(first + x), *(first + y));
    });
    return i;
}

template <typename, template <typename> typename, typename = void_t<>>
struct detect : false_type {};
template <typename T, template <typename> typename Check>
struct detect<T, Check, void_t<Check<T>>> : true_type {};
template <typename T, template <typename> typename Check>
constexpr inline bool detect_v = detect<T, Check>::value;

template <typename T>
using has_member_sort = decltype(declval<T>().sort());

template <typename Container, typename Compare = less<typename Container::value_type>>
auto sorted(Container c, Compare comp = Compare()) {
    if constexpr (detect_v<Container, has_member_sort>) {
        c.sort(comp);
        return c;
    }
    else {
        sort(begin(c), end(c), comp);
        return c;
    }
}

template <typename Container, typename Compare = equal_to<typename Container::value_type>>
auto uniqued(Container c, Compare comp = Compare()) {
    c.erase(unique(begin(c), end(c), comp), end(c));
    return c;
}

template <typename T, typename Compare = less<T>>
T &chmin(T &l, T r, Compare &&f = less<T>()) { return l = min(l, r, f); }
template <typename T, typename Compare = less<T>>
T &chmax(T &l, T r, Compare &&f = less<T>()) { return l = max(l, r, f); }

constexpr auto lim = 1000;

bool dp[lim + 1][lim + 1];

int main() {
    int n, k; cin >> n >> k;
    auto c = vec<int>(0, k + 1);
    for (int i = 0; i < n; ++i) {
        int a; cin >> a; ++c[a];
    }

    if (lim < k) {
        return 0;
    }

    int ans = 0;

    queue<int> que;

    bool all = true;
    for (int i = 0; i <= k; ++i) {
        if (c[i] == 0) {
            continue;
        }
        --c[i];

        fill(&dp[0][0], &dp[k][k] + 1, false);

        dp[0][0] = true;
        for (int j = 1; j <= k; ++j) {
            for (int x = 0; x <= k; ++x) {
                dp[j][x] = dp[j - 1][x];
                if (dp[j - 1][x]) {
                    que.push(x);
                }
            }

            for (int x = 0; x < c[j] && !empty(que); ++x) {
                int s = size(que);
                while (s--) {
                    int v = que.front(); que.pop();
                    if (v + j <= k && !dp[j][v + j]) {
                        dp[j][v + j] = true;
                        que.push(v + j);
                    }
                }
            }

            while (!empty(que)) {
                que.pop();
            }
        }

        ++c[i];

        all &= !dp[k][k - i];
        if (!dp[k][k] && dp[k][k - i]) {
            ans += c[i];
        }
    }

    if (!all) {
        cout << ans << endl;
    }
    else {
        cout << -1 << endl;
    }
}