#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 998244353;
// constexpr int MOD = 1000000007;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  constexpr int B = 30;
  int n; ll k; cin >> n >> k;
  vector<int> a(n);
  for (int& a_i : a) cin >> a_i;
  ranges::sort(a);
  const auto calc_mid = [&](const int l, const int r, const int bit) -> int {
    int mid = l;
    while ((a[mid] >> bit & 1) == 0 && mid <= r) ++mid;
    return mid;
  };
  vector<pair<int, int>> segs{{0, n - 1}};
  vector<tuple<int, int, int, int>> nsegs;
  int bit = B - 1, ans = 0;
  for (; bit >= 0; --bit) {
    vector<pair<int, int>> tmp;
    ll num = 0;
    for (const auto& [l, r] : segs) {
      const int mid = calc_mid(l, r, bit);
      num += (mid - l) * (mid - l - 1LL) / 2;
      num += (r - mid + 1LL) * (r - mid) / 2;
      if (l < mid - 1) tmp.emplace_back(l, mid - 1);
      if (mid < r) tmp.emplace_back(mid, r);
      if (l <= mid - 1 && mid <= r) nsegs.emplace_back(l, mid - 1, mid, r);
    }
    if (num < k) {
      k -= num;
      ans = 1 << bit;
      --bit;
      break;
    }
    segs.swap(tmp);
    nsegs.clear();
  }
  vector<tuple<int, int, int, int>> tmp1, tmp2;
  for (; bit >= 0; --bit) {
    tmp1.clear();
    tmp2.clear();
    ll num = 0;
    for (const auto& [xl, xr, yl, yr] : nsegs) {
      const int lmid = calc_mid(xl, xr, bit);
      const int rmid = calc_mid(yl, yr, bit);
      num += ll{lmid - xl} * (rmid - yl);
      num += (xr - lmid + 1LL) * (yr - rmid + 1LL);
      if (xl <= lmid - 1 && yl <= rmid - 1) tmp1.emplace_back(xl, lmid - 1, yl, rmid - 1);
      if (lmid <= xr && rmid <= yr) tmp1.emplace_back(lmid, xr, rmid, yr);
      if (xl <= lmid - 1 && rmid <= yr) tmp2.emplace_back(xl, lmid - 1, rmid, yr);
      if (lmid <= xr && yl <= rmid - 1) tmp2.emplace_back(lmid, xr, yl, rmid - 1);
    }
    if (num < k) {
      k -= num;
      ans |= 1 << bit;
      nsegs.swap(tmp2);
    } else {
      nsegs.swap(tmp1);
    }
  }
  cout << ans << '\n';
  return 0;
}