#include <cmath>
#include <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
priority_queue<int,vector<int>,greater<int> >q;
priority_queue<int >Q;
int n,m;
int num[100010];
int main()
{
	freopen("xorxor.in","r",stdin);
	freopen("xorxor.out","w",stdout);
	cin>>n>>m;
	for(int i=1;i<=n;i++)
	{
		cin>>num[i];
	}
	sort(num+1,num+n+1);
	for(int i=1;i<=n;i++)
	{
		for(int j=i+1;j<=n;j++)
		{
			Q.push(num[i]^num[j]);
		}
	}
	for(int i=1;i<=(n*(n-1)/2-m+1);i++)
	{
		Q.pop();
	}
	int ans=Q.top();
	cout<<ans<<endl;
	return 0;
}