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

struct BinaryTrie{
    //バグあるかもよ.
    struct Node{
        int times;
        int lazy;
        Node *LR[2];
        Node():times(0),lazy(0),LR{nullptr,nullptr}{}
    };
    private:
    int B = 30; //2^B未満の数のみ.
    Node *root = nullptr;
    void eval(Node *p,int &b){
        if(p->lazy&(1LL<<b)) swap(p->LR[0],p->LR[1]);
        if(p->LR[0] != nullptr) p->LR[0]->lazy ^= p->lazy;
        if(p->LR[1] != nullptr) p->LR[1]->lazy ^= p->lazy;
        p->lazy = 0;
    }
 
    private:
    Node* insert(Node *p,int &x,int b){
        if(p == nullptr) p = new Node;
        p->times++;
        if(b < 0) return p;
        eval(p,b);
        bool one = (x&(1LL<<b))>0;
        p->LR[one] = insert(p->LR[one],x,b-1);
        return p;
    }
    public: 
    void insert(int x){root = insert(root,x,B-1);}
 
    private:
    int lowerbound(Node *p,int &x,int b){
        if(p == nullptr || b < 0) return 0;
        eval(p,b);
        bool one = (x&(1LL<<b))>0;
        if(one && p->LR[0] != nullptr) return p->LR[0]->times+lowerbound(p->LR[one],x,b-1);
        return lowerbound(p->LR[one],x,b-1);
    }
    public:
    int lower_bound(int x){return lowerbound(root,x,B-1);}
    int upper_bound(int x){x++; return lowerbound(root,x,B-1);}
 
    public:
    void Xorall(int x){if(root != nullptr) root->lazy ^= x;}
};

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    long long N,K; cin >> N >> K;
    vector<int> A(N);
    for(auto &a : A) cin >> a;

    int low = -1,high = (1<<30)-1;
    while(high-low > 1){
        int mid = (high+low)/2;
        long long now = 0;
        BinaryTrie Z;
        for(int i=0; i<N; i++){
            Z.Xorall(A.at(i));
            int ok = Z.upper_bound(mid);
            now += ok;
            Z.Xorall(A.at(i));
            Z.insert(A.at(i));
        }
        if(now < K) low = mid;
        else high = mid;
    }
    cout << high << "\n";
}