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

struct BinaryTrie{
    //バグあるかもよ.
    struct Node{
        int times;
        long long 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;
    }
    public: void make(int b){B = b;}
 
    private:
    Node* insert(Node *p,long long &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(long long x){root = insert(root,x,B-1);}
    bool insertset(long long x){
        if(find(x) == 0) insert(x);
        else return false;
        return true;
    }
 
    private:
    Node* erase(Node *p,long long &x,int b){
        assert(p != nullptr);
        p->times--;
        if(p->times == 0) return nullptr;
        if(b < 0) return p;
        eval(p,b);
        bool one = (x&(1LL<<b))>0;
        p->LR[one] = erase(p->LR[one],x,b-1);
        return p;
    }
    public:
    void erase(long long x){root = erase(root,x,B-1);}
    bool eraseset(long long x){
        if(find(x) != 0) erase(x);
        else return false;
        return true;
    }
 
    private:
    long long getkth(Node *p,int k,int b){ //0-indexed.
        if(b < 0) return 0;
        eval(p,b);
        int L = 0;
        if(p->LR[0] != nullptr) L = p->LR[0]->times;
        return k<L?getkth(p->LR[0],k,b-1):getkth(p->LR[1],k-L,b-1)|(1LL<<b);
    }
    public: 
    long long getkth(int k){
        if(!(0 <= k && k < size())){
            cout << size() << endl; 
        }
        assert(0 <= k && k < size());
        return getkth(root,k,B-1);
    }
    long long getmin(long long x){
        Xorall(x);
        long long ret = getkth(0);
        Xorall(x); return ret;
    }
    long long getmax(long long x){
        Xorall(x);
        long long ret = getkth(size()-1);
        Xorall(x); return ret;
    }
 
    private:
    int lowerbound(Node *p,long long &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(long long x){return lowerbound(root,x,B-1);}
    int upper_bound(long long x){x++; return lowerbound(root,x,B-1);}
 
    public:
    int size(){
        if(root != nullptr) return root->times;
        else return 0;
    }
    void Xorall(long long x){if(root != nullptr) root->lazy ^= x;}
    int find(long long &x){
        if(root == nullptr) return 0;
        Node *p = root;
        for(int i=B-1; i>=0; i--){
            eval(p,i);
            p = p->LR[(x>>i)&1];
            if(p == nullptr) return 0;
        }
        return p->times;
    }
};

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";
}