#include<iostream>
#include<cstdio>
#include<cmath> 
#include<queue> 
using namespace std;
int n,k;
priority_queue<int> q;
int a[100001];
int main(){
	freopen("xorxor.in","r",stdin);
	freopen("xorxor.out","w",stdout);
	scanf("%d%d",&n,&k);
	for(int i=1;i<=n;i++)
	   scanf("%d",&a[i]);
	for(int j=1;j<=n;j++)
	   for(int v=j+1;v<=n;v++)
	     q.push(a[j] xor a[v]);
	for(int i=1;i<=n*(n-1)/2-k;i++)
	   q.pop();
	cout<<q.top();
	return 0;
}