/**
	author:  shobonvip
	created: 2024.12.11 04:03:07
**/

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

//* ATCODER
#include<atcoder/all>
using namespace atcoder;
typedef modint998244353 mint;
//*/

/* BOOST MULTIPRECISION
#include<boost/multiprecision/cpp_int.hpp>
using namespace boost::multiprecision;
//*/

typedef long long ll;

#define rep(i, s, n) for (int i = (int)(s); i < (int)(n); i++)
#define rrep(i, s, n) for (int i = (int)(n)-1; i >= (int)(s); i--)
#define all(v) v.begin(), v.end()

template <typename T> bool chmin(T &a, const T &b) {
	if (a <= b) return false;
	a = b;
	return true;
}

template <typename T> bool chmax(T &a, const T &b) {
	if (a >= b) return false;
	a = b;
	return true;
}

template <typename T> T max(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmax(ret, a[i]);
	return ret;
}

template <typename T> T min(vector<T> &a){
	assert(!a.empty());
	T ret = a[0];
	for (int i=0; i<(int)a.size(); i++) chmin(ret, a[i]);
	return ret;
}

template <typename T> T sum(vector<T> &a){
	T ret = 0;
	for (int i=0; i<(int)a.size(); i++) ret += a[i];
	return ret;
}

int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	
	ll n, k; cin >> n >> k;
	k--;
	vector<ll> a(n);
	rep(i,0,n) cin >> a[i];

	ll decided = 0;
	rrep(d,0,31) {
		ll tmp = 0;
		vector<map<ll,ll>> mp(2);
		rep(i,0,n) {
			ll f = a[i] >> (d + 1);
			tmp += mp[(a[i] >> d) & 1][f ^ decided];
			mp[(a[i] >> d) & 1][f] += 1;
		}
		if (tmp > k) {
			decided = decided * 2;
		}else{
			decided = decided * 2 + 1;
			k -= tmp;
		}
	}
	cout << decided << endl;
}