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

template <int LOG = 30> struct BinaryTrie {
    struct Node {
        long long cnt = 0;
        int ch[2] = {-1, -1};
    };
    std::vector<Node> ns;
    BinaryTrie() : ns(1) {}
    long long size() const { return ns[0].cnt; }
    long long operator[](int k) const { return find_kth(k, 0); }
    long long find_kth(long long k, long long xor_add = 0) const {
        assert(0 <= k && k < size());
        long long idx = 0, val = 0;
        for(int i=LOG-1; i>=0; i--) {
            long long c = xor_add >> i & 1;
            long long low_ch = ns[idx].ch[c];
            long long low_cnt = (low_ch >= 0 ? ns[low_ch].cnt : 0);
            if (k < low_cnt) {
                idx = low_ch;
            } else {
                k -= low_cnt;
                idx = ns[idx].ch[c ^ 1];
                val ^= 1LL << i;
            }
            assert(idx >= 0);
        }
        return val;
    }
    void add(long long val, long long cnt = 1) {
        assert(0 <= val && val < (1LL << LOG));
        int idx = 0;
        for(int i=LOG-1; i>=0; i--) {
            ns[idx].cnt += cnt;
            assert(ns[idx].cnt >= 0);
            int &nxt = ns[idx].ch[val >> i & 1];
            if (nxt == -1) {
                idx = nxt = ns.size();
                ns.emplace_back();
            } else {
                idx = nxt;
            }
        }
        ns[idx].cnt += cnt;
        assert(ns[idx].cnt >= 0);
    }
    long long lower_bound(long long val, long long xor_add = 0) {
        assert(0 <= val);
        if (val >= (1LL << LOG)) return size();
        int idx = 0;
        long long cnt = 0;
        for(int i=LOG-1; i>=0; i--) {
            int b = val >> i & 1, c = xor_add >> i & 1;
            int ch = ns[idx].ch[c];
            cnt += (b & (ch >= 0) ? ns[ch].cnt : 0);
            idx = ns[idx].ch[b ^ c];
            if (idx < 0 or ns[idx].cnt == 0) break;
        }
        return cnt;
    }
    long long count(long long val) const {
        assert(0 <= val && val < (1LL << LOG));
        int idx = 0;
        for(int i=LOG-1; i>=0; i--) {
            idx = ns[idx].ch[val >> i & 1];
            if (idx < 0 or ns[idx].cnt == 0) return 0;
        }
        return ns[idx].cnt;
    }
    long long count(long long L, long long R, long long xor_add = 0) {
        assert(0 <= L && L <= R && R <= (1LL << LOG));
        return lower_bound(R, xor_add) - lower_bound(L, xor_add);
    }
    long long xor_min(long long xor_add = 0) { return find_kth(0, xor_add); }
    long long xor_max(long long xor_add = 0) { return find_kth(size() - 1, xor_add); }
};

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    ll k;
    cin >> n >> k;
    vector<int> a(n);
    BinaryTrie<30> trie;
    for(auto &&v : a){
        cin >> v;
        trie.add(v);
    }
    int ng = -1, ok = 1 << 30;
    while(ng + 1 < ok){
        int mid = (ok + ng) / 2;
        ll tot = -n;
        for(auto &&v : a) tot += trie.lower_bound(mid + 1, v);
        tot /= 2;
        (tot >= k ? ok : ng) = mid;
    }
    cout << ok << '\n';
}