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

using ll = long long;
bool deb = 1;

struct Binary_Trie {
    ll base = 36; // 桁数
    struct Node {
        ll next[2];
        ll c, num;
        Node(ll c_) : c(c_), num(0) {
            next[0] = next[1] = -1;
        }
    };

    vector<Node> nodes;
    ll root = 0;

    Binary_Trie() {
        nodes.push_back(Node(root));
    }

    void insert(const ll& num) {
        ll node_id = 0;
        for (ll b = base; b >= 0; b--) {
            ll nt = 0;
            nt = (num & (1ll << b) ? 1 : 0);
            if (nodes[node_id].next[nt] == -1) {
                nodes.push_back(Node(nt));
                nodes[node_id].next[nt] = nodes.size() - 1;
            }
            nodes[node_id].num++;
            node_id = nodes[node_id].next[nt];
        }
        nodes[node_id].num++;
    }

    bool search(const ll& num) {
        ll node_id = 0;
        bool EX = 1;
        for (ll b = base; b >= 0; b--) {
            ll nt = 0;
            nt = (num & (1ll << b) ? 1 : 0);
            if (nodes[node_id].next[nt] == -1 || nodes[nodes[node_id].next[nt]].num == 0) {
                EX = 0;
                break;
            }
            node_id = nodes[node_id].next[nt];
        }
        return EX;
    }

    void erase(const ll& num) {
        if (!search(num)) return;
        ll node_id = 0;
        for (ll b = base; b >= 0; b--) {
            ll nt = 0;
            nt = (num & (1ll << b) ? 1 : 0);
            nodes[node_id].num--;
            node_id = nodes[node_id].next[nt];
        }
        nodes[node_id].num--;
    }

    ll small_num(const ll& p, const ll& x) { // d XOR p < x なる d の個数
        ll res = 0;
        ll node_id = 0;
        for (ll b = base; b >= 0; b--) {
            ll nx = 0, np = 0;
            nx = (x & (1ll << b) ? 1 : 0);
            np = (p & (1ll << b) ? 1 : 0);
            if (nx == 1) {
                if (nodes[node_id].next[np] != -1) {
                    res += nodes[nodes[node_id].next[np]].num;
                }
                if (nodes[node_id].next[1 - np] == -1) {
                    break;
                } else {
                    node_id = nodes[node_id].next[1 - np];
                    continue;
                }
            } else {
                if (nodes[node_id].next[np] == -1) {
                    break;
                } else {
                    node_id = nodes[node_id].next[np];
                    continue;
                }
            }
        }
        return res;
    }

    ll min_XOR(ll x) {
        ll res = 0, node_id = 0;
        for (ll b = base; b >= 0; b--) {
            ll nx = 0;
            nx = (x & (1ll << b) ? 1 : 0);
            if (nodes[node_id].next[nx] != -1 && nodes[nodes[node_id].next[nx]].num > 0) {
                node_id = nodes[node_id].next[nx];
            } else {
                res += (1ll << b);
                node_id = nodes[node_id].next[1 - nx];
            }
        }
        return res;
    }

    ll K_thsmall(ll K) { // K番目に小さい値を返す.(0index)
        if (nodes[0].num <= K) return -1e18;
        ll node_id = 0, res = 0;
        for (ll b = base; b >= 0; b--) {
            if (nodes[node_id].next[0] != -1 && nodes[nodes[node_id].next[0]].num > K) {
                node_id = nodes[node_id].next[0];
            } else {
                res += (1ll << b);
                if (nodes[node_id].next[0] != -1) {
                    K -= nodes[nodes[node_id].next[0]].num;
                }
                node_id = nodes[node_id].next[1];
            }
        }
        return res;
    }
};



int main() {

    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    ll N=2e5;
    ll K=(N*(N-1))/4;
    cin>>N>>K;
    vector<ll> A(N);
    Binary_Trie B;
    for(int i=0;i<N;i++){
        cin>>A[i];
        // A[i]=rand()%ll(1e9);
        B.insert(A[i]);
    }
    ll L=-1,R=4e9;
    while(R-L>1){
        ll M=(R+L)/2;
        ll cnt=0;
        if(M!=0)for(int i=0;i<N;i++){
            cnt+=B.small_num(A[i],M)-1;
        }
        (cnt/2<K?L:R)=M;
    }
    cout<<L<<endl;
}