#include <bits/stdc++.h>
using namespace std;
priority_queue<int,vector<int>,greater<int> >q;
int n, k, a[50001000];

inline char get_char(){
	static char buf[28670], *p1=buf, *p2=buf;
    return p1==p2&&(p2=(p1=buf)+fread(buf,1,28670,stdin),p1==p2)?EOF:*p1++;
}
inline int read() 
{
	int x=0, f=0; char ch=get_char();
	while(ch<'0'||ch>'9') {f|=(ch=='-'); ch=get_char();}
	while(ch>='0'&&ch<='9') {x=(x<<3)+(x<<1)+(ch^48); ch=get_char();}
	return f?-x:x;
}
int main()
{
	freopen("xorxor.in","r",stdin);
	freopen("xorxor.out","w",stdout);
	n=read(), k=read();
	for(register int i=1; i<=n; ++i) {a[i]=read();}
	for(register int i=1; i<=n; ++i)
	{
		for(register int j=i+1; j<=n; ++j)
		{
			q.push(a[i]^a[j]);
		}
	}
	while(--k)
	{
		q.pop();
	}
	printf("%d\n",q.top());
	fclose(stdin);
	fclose(stdout);
	return 0;
}