#include<bits/stdc++.h>
using namespace std;
int n,k,a[10000005],i,j,cnt,b[100005];
bool cmp(int c,int b){
	return c<b;
}
inline void init(){
	freopen("xorxor.in","r",stdin);
	freopen("xorxor.out","w",stdout);
}
inline void end(){
	fclose(stdin);
	fclose(stdout); 
}
int main(){
	init();
	scanf("%d%d",&n,&k);
	for(i=1;i<=n;++i)scanf("%d",&b[i]);
	for(i=1;i<=n;++i){
		for(j=i+1;j<=n;++j){
			a[++cnt]=b[i]^b[j];
		}
	}
	sort(a+1,a+1+cnt,cmp);
	printf("%d",a[k]);
	end();
	return 0;
}