#include<bits/stdc++.h>
using namespace std;
 
#define NUM ch-'0'
inline void read(int &res){
	char ch;
	bool flag=0;
	while(!isdigit(ch=getchar()))
		(flag=1)&&(ch=='-');
	for(res=NUM;isdigit(ch=getchar());res=res*10+NUM);
	(flag)&&(res=-res);
}
const int MAXN = 50000+2;
int a[MAXN];
int b[MAXN*10];
 
void file(){
	freopen("xorxor.in","r",stdin);
	freopen("xorxor.out","w",stdout);
}
 
int main(){
	file();
	int n,m;
	read(n);
	read(m);
	for(int i=1;i<=n;++i){
		read(a[i]);
	}
	int p=0;
	for(int i=1;i<n;++i){
		for(int j=i+1;j<=n;++j){
			b[++p] = a[i]^a[j];
		}
	}
	sort(b+1,b+p+1);
	printf("%d",b[m]);
}