#include<iostream>
#include<cstring>
#include<cstdio> 
#include<algorithm>
#include<queue>
using namespace std;
const int maxn=100000+1000;

priority_queue<int> q;
long long a[maxn],n,k;

int main(){
	freopen("xorxor.in","r",stdin);
	freopen("xorxor.out","w",stdout);
	cin>>n>>k;
	for(int i=0;i<n;i++)
		cin>>a[i];
	for(int i=0,x;i<n;i++){
		for(int j=i+1;j<n;j++){
			x=a[i]^a[j];
			q.push(-x);
		}
	}
	for(int i=0;i<k-1;i++)q.pop();
	cout<<-q.top();
	return 0;
}