#include<iostream>
#include<cstdio>
#include<algorithm>
#include<vector>
#include<queue>
#include<cstring>
using namespace std;

int read()
{
    int f=1,x=0;
    char ss=getchar();
    while(ss<'0'||ss>'9'){if(ss=='-')f=-1;ss=getchar();}
    while(ss>='0'&&ss<='9'){x=x*10+ss-'0';ss=getchar();}
    return x*f;
}

void print(int x)
{
    if(x<0){putchar('-');x=-x;}
    if(x>9)print(x/10);
    putchar(x%10+'0');
}  

int n,k;
int a[1000010];
priority_queue<int, vector<int>, greater<int> >q;

int main()
{
	freopen("xorxor.in","r",stdin);
	freopen("xorxor.out","w",stdout);
	
	n=read();k=read();
	for(int i=1;i<=n;i++)
	a[i]=read();
	
	for(int i=1;i<=n;i++)
	{
		for(int j=1;j<i;j++)
		{
			if(i==j)continue;
			q.push(a[i]^a[j]);
		}
	}
	k--;
	while(k--)
	q.pop();
	
	print(q.top());
	
	fclose(stdin);
	fclose(stdout);
	return 0;
}