#include <cstdio>
#include <iostream>
#include <queue>
using namespace std;
class priority_queue<int,vector<int>,greater<int> > que;
int num[100000004];
int main()
{
	freopen("xorxor.in","r",stdin);
	freopen("xorxor.out","w",stdout);
	int n,k;
	cin>>n>>k;;
	for(int i=1;i<=n;i++)
		cin>>num[i];
	for(int i=1;i<=n;i++)
		for(int j=i+1;j<=n;j++)
			que.push(num[i]^num[j]);
	for(int i=1;i<k;i++)
		que.pop();
	cout<<que.top();
	fclose(stdin);
	fclose(stdout);
	return 0;
}