#include<iostream>
#include<cstdio>
#include<cstring>
#include<vector>
#include<algorithm>
using namespace std;
int n,k,a[100005];
vector<int>ans;
void init(){
	scanf("%d%d",&n,&k);
	for(int i=1;i<=n;i++) scanf("%d",&a[i]);
}
void solve30(){
	for(int i=1;i<=n-1;i++)
	for(int j=i+1;j<=n;j++){
		ans.push_back(a[i]^a[j]);
	}
	
	sort(ans.begin(),ans.end());
	
	printf("%d",ans[k-1]);//变长数组是从0开始的 
}
int main(){
	freopen("xorxor.in","r",stdin);
	freopen("xorxor.out","w",stdout);
	init();
	
    solve30();
	
	return 0;
}