#include <bits/stdc++.h>
#include <bits/stdc++.h>
#include <bits/stdc++.h>
using namespace std;
// #include <atcoder/modint>
// using namespace atcoder;
// using mint = modint998244353;
using ll = long long;
#define fix(x) fixed << setprecision(x)
#define rep(i, n) for(int i = 0; i < n; ++i)
#define all(x) (x).begin(),(x).end()
template<class T>bool chmin(T&a, const T&b){if(a>b){a=b;return 1;}return 0;}
template<class T>bool chmax(T&a, const T&b){if(a<b){a=b;return 1;}return 0;}
constexpr ll INFLL = (1LL << 62), MOD = 998244353;
constexpr int INF = (1 << 30);

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    ll n,k;
    cin >> n >> k;
    k = k * 2 + n - 1;
    vector<int> a(n);
    rep(i,n) cin >> a[i];
    int ans = 0, mask = 0;
    for(int i=29;i>=0;--i){
        mask |= 1<<i;
        map<int,ll> mp;
        ll cnt = 0;
        rep(j,n) ++mp[mask&a[j]];
        for(auto [p,q]:mp){
            cnt += q * mp[p^ans];
        }
        if(cnt<=k){
            k -= cnt;
            ans |= (1<<i);
        }
    }
    cout << ans << '\n';
    return 0;
}