#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
 
int n,k,s[550],a[124755],g;
 
int main()
{
	freopen("xorxor.in","r",stdin);
	freopen("xorxor.out","w",stdout);
	scanf("%d %d",&n,&k);
	scanf("%d",&s[0]);
	for(int i=1;i<n;i++)
	{
		scanf("%d",&s[i]);
		for(int j=0;j<i;j++)
		{
			a[g]=s[j]^s[i];
			g++;
		}
	}
	sort(a+0,a+g);
	k--;
	printf("%d",a[k]);
	return 0;
}