#include <iostream>
#include <cstring>
#include <algorithm>
#include <cstdio>
#include <queue>
#define maxn 500000 + 10
using namespace std;
int n,k;
int a[maxn],vis[maxn];
priority_queue<int> q;
int main()
{
	freopen("xorxor.in","r",stdin);
	freopen("xorxor.out","w",stdout);
    int cnt = 0;
	scanf("%d%d",&n,&k);
	for(int i = 1; i <= n; i++)
	    scanf("%d",&a[i]);
	for(int i = 1; i <= n - 1; i++)
	   for(int j = i + 1; j <= n; j++)
	      {
	      	int x = (a[i] xor a[j]);
	      	if(!vis[x]) q.push(-x),vis[x]++;
	      	else vis[x]++;
		  }
	      	
	while(cnt < k) 
	{
		if(cnt + vis[-q.top()] >= k) break;
		else cnt += vis[-q.top()],q.pop();
	}
	printf("%d",-q.top());
	return 0;
}