#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define inf 4000000000000000000
#define mod 998244353
#define siz 524288
set < pair < ll, ll > > s;
priority_queue < pair < ll, ll > > pq;
ll a[200005],v[200005],ncnt = 1;
struct Node
{
ll v,idx;
};
struct Tree
{
ll left = 2000001,right = 2000001,sz = 0;
vector < ll > e;
}trie[2000005];
void update(ll node,ll v,ll idx,ll cnt)
{
if(cnt == -1)
{
//printf("%lld\n",node);
trie[node].e.push_back(idx);
trie[node].sz++;
return;
}
if(v & (1LL<<cnt))
{
if(trie[node].left == 2000001)trie[node].left = ncnt++;
update(trie[node].left,v,idx,cnt-1);
trie[node].sz = trie[trie[node].left].sz + trie[trie[node].right].sz;
}
else
{
if(trie[node].right == 2000001)trie[node].right = ncnt++;
update(trie[node].right,v,idx,cnt-1);
trie[node].sz = trie[trie[node].left].sz + trie[trie[node].right].sz;
}
}
ll query(ll node,ll v,ll cnt,ll nv)
{
if(cnt == -1)return trie[node].sz;
ll ret = 0;
if(nv & (1LL<<cnt))
{
if(v & (1LL<<cnt))ret += trie[trie[node].left].sz;
else ret += trie[trie[node].right].sz;
if(v & (1LL<<cnt))return ret + query(trie[node].right,v,cnt-1,nv);
else return ret + query(trie[node].left,v,cnt-1,nv);
}
if(v & (1LL<<cnt))return query(trie[node].left,v,cnt-1,nv);
else return query(trie[node].right,v,cnt-1,nv);
}
bool can(ll mid,ll n,ll k)
{
ll i,nans = 0;
for(i=1;i<=n;i++)
{
nans += query(0,a[i],31,mid) - 1;
}
return nans >= 2 * k;
}
ll bs(ll s,ll e,ll n,ll k)
{
if(s == e)return s;
ll mid = (s+e)/2;
if(can(mid,n,k))return bs(s,mid,n,k);
return bs(mid+1,e,n,k);
}
int main()
{
ll i,j,k,n,m,ans = 0;
scanf("%lld %lld",&n,&m);
for(i=1;i<=n;i++)
{
scanf("%lld",&a[i]);
update(0,a[i],i,31);
v[i] = 1;
}
printf("%lld",bs(0,(1LL<<31LL),n,m));
}
