#line 1 "test.cpp"
#include<bits/stdc++.h>
using namespace std;
// #pragma GCC target("avx,avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")
#ifdef LOCAL
#include <debug.hpp>
#define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#define debug(...) (static_cast<void>(0))
#endif
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pll = pair<ll,ll>;
using pii = pair<int,int>;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vul = vector<ull>;
using vpii = vector<pii>;
using vvpii = vector<vpii>;
using vpll = vector<pll>;
using vs = vector<string>;
template<class T> using pq = priority_queue<T,vector<T>, greater<T>>;
#define overload4(_1, _2, _3, _4, name, ...) name
#define overload3(a,b,c,name,...) name
#define rep1(n) for (ll UNUSED_NUMBER = 0; UNUSED_NUMBER < (n); ++UNUSED_NUMBER)
#define rep2(i, n) for (ll i = 0; i < (n); ++i)
#define rep3(i, a, b) for (ll i = (a); i < (b); ++i)
#define rep4(i, a, b, c) for (ll i = (a); i < (b); i += (c))
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)
#define rrep1(n) for(ll i = (n) - 1;i >= 0;i--)
#define rrep2(i,n) for(ll i = (n) - 1;i >= 0;i--)
#define rrep3(i,a,b) for(ll i = (b) - 1;i >= (a);i--)
#define rrep4(i,a,b,c) for(ll i = (a) + ((b)-(a)-1) / (c) * (c);i >= (a);i -= c)
#define rrep(...) overload4(__VA_ARGS__, rrep4, rrep3, rrep2, rrep1)(__VA_ARGS__)
#define all1(i) begin(i) , end(i)
#define all2(i,a) begin(i) , begin(i) + a
#define all3(i,a,b) begin(i) + a , begin(i) + b
#define all(...) overload3(__VA_ARGS__, all3, all2, all1)(__VA_ARGS__)
#define sum(...) accumulate(all(__VA_ARGS__),0LL)
template<class T> bool chmin(T &a, const T &b){ if(a > b){ a = b; return 1; } else return 0; }
template<class T> bool chmax(T &a, const T &b){ if(a < b){ a = b; return 1; } else return 0; }
template<class T> auto min(const T& a){return *min_element(all(a));}
template<class T> auto max(const T& a){return *max_element(all(a));}
template<class... Ts> void in(Ts&... t);
#define INT(...) int __VA_ARGS__; in(__VA_ARGS__)
#define LL(...) ll __VA_ARGS__; in(__VA_ARGS__)
#define STR(...) string __VA_ARGS__; in(__VA_ARGS__)
#define CHR(...) char __VA_ARGS__; in(__VA_ARGS__)
#define DBL(...) double __VA_ARGS__; in(__VA_ARGS__)
#define LD(...) ld __VA_ARGS__; in(__VA_ARGS__)
#define VEC(type, name, size) vector<type> name(size); in(name)
#define VV(type, name, h, w) vector<vector<type>> name(h, vector<type>(w)); in(name)
ll intpow(ll a, ll b){ll ans = 1; while(b){if(b & 1) ans *= a; a *= a; b /= 2;} return ans;}
ll modpow(ll a, ll b, ll p){ ll ans = 1; a %= p;if(a < 0) a += p;while(b){ if(b & 1) (ans *= a) %= p; (a *= a) %= p; b /= 2; } return ans; }
bool is_clamp(ll val,ll low,ll high) {return low <= val && val < high;}
void Yes() {cout << "Yes\n";return;}
void No() {cout << "No\n";return;}
void YES() {cout << "YES\n";return;}
void NO() {cout << "NO\n";return;}
template <typename T>
T floor(T a, T b) {return a / b - (a % b && (a ^ b) < 0);}
template <typename T>
T ceil(T x, T y) {return floor(x + y - 1, y);}
template <typename T>
T bmod(T x, T y) {return x - y * floor(x, y);}
template <typename T>
pair<T, T> divmod(T x, T y) {T q = floor(x, y);return {q, x - q * y};}
namespace IO{
#define VOID(a) decltype(void(a))
struct setting{ setting(){cin.tie(nullptr); ios::sync_with_stdio(false);fixed(cout); cout.precision(15);}} setting;
template<int I> struct P : P<I-1>{};
template<> struct P<0>{};
template<class T> void i(T& t){ i(t, P<3>{}); }
void i(vector<bool>::reference t, P<3>){ int a; i(a); t = a; }
template<class T> auto i(T& t, P<2>) -> VOID(cin >> t){ cin >> t; }
template<class T> auto i(T& t, P<1>) -> VOID(begin(t)){ for(auto&& x : t) i(x); }
template<class T, size_t... idx> void ituple(T& t, index_sequence<idx...>){in(get<idx>(t)...);}
template<class T> auto i(T& t, P<0>) -> VOID(tuple_size<T>{}){ituple(t, make_index_sequence<tuple_size<T>::value>{});} 
#undef VOID
}
#define unpack(a) (void)initializer_list<int>{(a, 0)...}
template<class... Ts> void in(Ts&... t){ unpack(IO :: i(t)); }
#undef unpack
constexpr long double PI = 3.141592653589793238462643383279L;
template <class F> struct REC {
    F f;
    REC(F &&f_) : f(forward<F>(f_)) {}
    template <class... Args> auto operator()(Args &&...args) const { return f(*this, forward<Args>(args)...); }};

constexpr int mod = 998244353;
//constexpr int mod = 1000000007;

#line 1 "library/data-structure/binarytrie.hpp"
// MAX_LOG 2^(MAX_LOG)までの値がOK
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;
  }
};
#line 101 "test.cpp"
int main() {
    INT(n);
    LL(k);
    VEC(int,a,n);
    BinaryTrie<int,30> BT;
    rep(i,n) BT.add(a[i]);
    ll ng = -1,ok = 1 << 30;
    while(ok - ng > 1) {
        ll mid = (ng + ok) / 2;
        ll cnt = 0;
        rep(i,n) {
            debug(mid,i,BT.count_less(mid+1,a[i]) - 1);
            cnt += BT.count_less(mid+1,a[i]) - 1;
        }
        if(cnt >= 2 * k) ok = mid;
        else ng = mid;
    }
    cout << ok << '\n';
}