#include <bits/stdc++.h>

using namespace std;

#define overload4(_1, _2, _3, _4, name, ...) name
#define rep1(n) for(int i = 0; i < (int)(n); ++i)
#define rep2(i, n) for(int i = 0; i < (int)(n); ++i)
#define rep3(i, a, b) for(int i = (a); i < (int)(b); ++i)
#define rep4(i, a, b, c) for(int i = (a); i < (int)(b); i += (c))
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)

#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; --i)
#define ALL(a) (a).begin(), (a).end()
#define Sort(a) (sort((a).begin(), (a).end()))
#define RSort(a) (sort((a).rbegin(), (a).rend()))
#define UNIQUE(a) (a.erase(unique((a).begin(), (a).end()), (a).end()))

typedef long long int ll;
typedef unsigned long long ul;
typedef long double ld;
typedef vector<int> vi;
typedef vector<long long> vll;
typedef vector<char> vc;
typedef vector<string> vst;
typedef vector<double> vd;
typedef vector<long double> vld;
typedef pair<long long, long long> P;

template<class T> long long sum(const T &a){ return accumulate(a.begin(), a.end(), 0LL); }
template<class T> auto min(const T &a){ return *min_element(a.begin(), a.end()); }
template<class T> auto max(const T &a){ return *max_element(a.begin(), a.end()); }

const long long MINF = 0x7fffffffffff;
const long long INF = 0x1fffffffffffffff;
const long long MOD = 998244353;
const long double EPS = 1e-9;
const long double PI = acos(-1);

template<class T> inline bool chmax(T &a, T b) { if(a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T &a, T b) { if(a > b) { a = b; return 1; } return 0; }

template<typename T1, typename T2> istream &operator>>(istream &is, pair<T1, T2> &p){ is >> p.first >> p.second; return is; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p){ os << "(" << p.first << ", " << p.second << ")"; return os; }
template<typename T> istream &operator>>(istream &is, vector<T> &v){ for(T &in : v) is >> in; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &v){ for(int i = 0; i < (int) v.size(); ++i){ os << v[i] << (i + 1 != (int) v.size() ? " " : ""); } return os; }
template <typename T, typename S> ostream &operator<<(ostream &os, const map<T, S> &mp){ for(auto &[key, val] : mp){ os << key << ":" << val << " "; } return os; }
template <typename T> ostream &operator<<(ostream &os, const set<T> &st){ auto itr = st.begin(); for(int i = 0; i < (int) st.size(); ++i){ os << *itr << (i + 1 != (int) st.size() ? " " : ""); itr++; } return os; }
template <typename T> ostream &operator<<(ostream &os, const multiset<T> &st){ auto itr = st.begin(); for(int i = 0; i < (int) st.size(); ++i){ os << *itr << (i + 1 != (int) st.size() ? " " : ""); itr++; } return os; }
template <typename T> ostream &operator<<(ostream &os, queue<T> q){ while(q.size()){ os << q.front() << " "; q.pop(); } return os; }
template <typename T> ostream &operator<<(ostream &os, deque<T> q){ while(q.size()){ os << q.front() << " "; q.pop_front(); } return os; }
template <typename T> ostream &operator<<(ostream &os, stack<T> st){ while(st.size()){ os << st.top() << " "; st.pop(); } return os; }
template <class T, class Container, class Compare> ostream &operator<<(ostream &os, priority_queue<T, Container, Compare> pq){ while(pq.size()){ os << pq.top() << " "; pq.pop(); } return os; }

template <typename T>
long long binary_search(long long ok, long long ng, T check){
    while(abs(ok - ng) > 1){
        long long mid = (ok + ng) / 2;
        if(check(mid)) ok = mid;
        else ng = mid;
    }
    return ok;
}

template <typename T>
long double binary_search_real(long double ok, long double ng, T check, int iter = 100){
    for(int i = 0; i < iter; ++i){
        long double mid = (ok + ng) / 2;
        if(check(mid)) ok = mid;
        else ng = mid;
    }
    return ok;
}

template <typename T>
long long trisum(T a, T b){
    long long res = ((b - a + 1) * (a + b)) / 2;
    return res;
}

template <typename T>
T intpow(T x, int n){
    T ret = 1;
    while(n > 0) {
        if(n & 1) (ret *= x);
        (x *= x);
        n >>= 1;
    }
    return ret;
}

template <typename T>
T getReminder(T a, T b){
    if(b == 0) return -1;
    if(a >= 0 && b > 0){
        return a % b;
    } else if(a < 0 && b > 0){
        return ((a % b) + b) % b;
    } else if(a >= 0 && b < 0){
        return a % b;
    } else{
        return (abs(b) - abs(a % b)) % b;
    }
}

template<class T, class U> inline T vin(T &vec, U n) { vec.resize(n); for(int i = 0; i < (int) n; ++i) cin >> vec[i]; return vec; }
template<class T> inline void vout(T vec, string s = "\n"){ for(auto x : vec) cout << x << s; }
template<class... T> void in(T&... a){ (cin >> ... >> a); }
void out(){ cout << '\n'; }
template<class T, class... Ts> void out(const T &a, const Ts&... b){ cout << a; (cout << ... << (cout << ' ', b)); cout << '\n'; }
template<class T, class U> void inGraph(vector<vector<T>> &G, U n, U m, bool directed = false){ G.resize(n); for(int i = 0; i < m; ++i){ int a, b; cin >> a >> b; a--, b--; G[a].push_back(b); if(!directed) G[b].push_back(a); } }

// https://ei1333.github.io/library/structure/trie/binary-trie.hpp.html
template <typename T, int MAX_LOG, typename D = int>
struct BinaryTrie {
 public:
  struct Node {
    Node *nxt[2];
    D exist;
    vector<int> accept;

    Node() : nxt{nullptr, nullptr}, exist(0) {}
  };

  Node *root;

  explicit BinaryTrie() : root(new Node()) {}

  explicit BinaryTrie(Node *root) : root(root) {}

  void add(const T &bit, int idx = -1, D delta = 1, T xor_val = 0) {
    root = add(root, bit, idx, MAX_LOG, delta, xor_val);
  }

  void erase(const T &bit, T xor_val = 0) { add(bit, -1, -1, xor_val); }

  Node *find(const T &bit, T xor_val = 0) {
    return find(root, bit, MAX_LOG, xor_val);
  }

  D count(const T &bit, T xor_val = 0) {
    auto node = find(bit, xor_val);
    return node ? node->exist : 0;
  }

  pair<T, Node *> min_element(T xor_val = 0) {
    assert(root->exist > 0);
    return kth_element(0, xor_val);
  }

  pair<T, Node *> max_element(T xor_val = 0) {
    assert(root->exist > 0);
    return kth_element(root->exist - 1, xor_val);
  }

  pair<T, Node *> kth_element(D k, T xor_val = 0) {  // 0-indexed
    assert(0 <= k && k < root->exist);
    return kth_element(root, k, MAX_LOG, xor_val);
  }

  D count_less(const T &bit, T xor_val = 0) {  // < bit
    return count_less(root, bit, MAX_LOG, xor_val);
  }

 private:
  virtual Node *clone(Node *t) { return t; }

  Node *add(Node *t, T bit, int idx, int depth, D x, T xor_val,
            bool need = true) {
    if (need) t = clone(t);
    if (depth == -1) {
      t->exist += x;
      if (idx >= 0) t->accept.emplace_back(idx);
    } else {
      bool f = (xor_val >> depth) & 1;
      auto &to = t->nxt[f ^ ((bit >> depth) & 1)];
      if (!to) to = new Node(), need = false;
      to = add(to, bit, idx, depth - 1, x, xor_val, need);
      t->exist += x;
    }
    return t;
  }

  Node *find(Node *t, T bit, int depth, T xor_val) {
    if (depth == -1) {
      return t;
    } else {
      bool f = (xor_val >> depth) & 1;
      auto &to = t->nxt[f ^ ((bit >> depth) & 1)];
      return to ? find(to, bit, depth - 1, xor_val) : nullptr;
    }
  }

  pair<T, Node *> kth_element(Node *t, D k, int bit_index,
                              T xor_val) {  // 0-indexed
    if (bit_index == -1) {
      return {0, t};
    } else {
      bool f = (xor_val >> bit_index) & 1;
      if ((t->nxt[f] ? t->nxt[f]->exist : 0) <= k) {
        auto ret =
            kth_element(t->nxt[f ^ 1], k - (t->nxt[f] ? t->nxt[f]->exist : 0),
                        bit_index - 1, xor_val);
        ret.first |= T(1) << bit_index;
        return ret;
      } else {
        return kth_element(t->nxt[f], k, bit_index - 1, xor_val);
      }
    }
  }

  D count_less(Node *t, const T &bit, int bit_index, T xor_val) {
    if (bit_index == -1) return 0;
    D ret = 0;
    bool f = (xor_val >> bit_index) & 1;
    if ((bit >> bit_index & 1) and t->nxt[f]) ret += t->nxt[f]->exist;
    if (t->nxt[f ^ (bit >> bit_index & 1)])
      ret += count_less(t->nxt[f ^ (bit >> bit_index & 1)], bit, bit_index - 1,
                        xor_val);
    return ret;
  }
};
ll T;

void input(){
    in(T);
}

void solve(){
    ll n, k; in(n, k);
    vll a(n); in(a);
    Sort(a);
    BinaryTrie<ll, 30> bt;
    rep(i, n) bt.add(a[i]);
    auto f = [&](ll x){
        ll s = 0;
        rep(i, n){
            if(s + (n * (n - i)) < k){
                return false;
            }
            s += bt.count_less(x + 1, a[i]);
            if(s >= (k * 2) + n){
                return true;
            }
        }
        return false;
    };
    out(binary_search(1LL << 30, -1LL, f));
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(20);

    T = 1;
    // input();
    while(T--) solve();
}