#include<bits/stdc++.h>
using namespace std;

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;

int main(){
	int N;cin>>N;
	long K;cin>>K;K--;

	vector<int> A(N);for(auto&&e:A)cin>>e;

	int S=0;

	for(int i=30;i>=0;i--){
		gp_hash_table<int, int> mp;

		for(auto&&e:A){
			mp[(e>>i)<<i]++;
		}

		long cnt=0;

		for(auto&&[e,c]:mp){
			if(e>(e^S))continue;
			if(S==0){
				cnt+=long(c)*(c-1)/2;
			}else{
				if(mp.find(e^S)!=mp.end()){
					cnt+=long(c)*mp[e^S];
				}
			}
		}

		if(cnt<=K){
			S|=1<<i;
			K-=cnt;
		}

	}

	cout<<S<<endl;
}