#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
#include<algorithm>
#include<cstdlib>
using namespace std;
typedef long long ll;
template <class E>inline void read(E &e){
	e=0;char c=getchar();bool eh=0;
	while(c>'9'||c<'0'){if(c=='-')eh=1;c=getchar();}
	while(c>='0'&&c<='9'){e=e*10+c-48;c=getchar();}
	if(eh) e=-e;
}
int a[20000000];
int e[5000000];
int main(){
	freopen("xorxor.in","r",stdin);
	freopen("xorxor.out","w",stdout);
	int n,k;
	read(n);read(k);
	int w=0;
	for(int i=1;i<=n;++i){
		read(e[i]);
	}
	for(int i=1;i<=n;++i){
		for(int j=i+1;j<=n;++j){
			a[++w]=e[i]^e[j];
		}
	} 
	sort(a+1,a+w+1);
	printf("%d\n",a[k]);
	return 0;
}