#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)

using namespace std;
using ll = long long;

int main() {
    cin.tie(nullptr) -> sync_with_stdio(false);
    
    int n; ll k;
    cin >> n >> k;
    --k;
    
    vector<int> a(n);
    rep(i, n) cin >> a[i];
    
    int ans = 0;
    for (int i = 30; i >= 0; --i) {
        map<int, int> mp;
        for (int x : a) mp[x>>i<<i]++;
        
        ll cnt = 0;
        for (auto [x, num] : mp) {
            if (x > (x^ans)) continue; 
            
            if (ans == 0) cnt += (ll)num*(num-1)/2;
            else {
                if (mp.count(x^ans)) cnt += (ll)num*mp[x^ans]; 
            }
        }
        
        if (cnt <= k) {
            ans |= 1<<i;
            k -= cnt;
        }
    }
    
    cout << ans << '\n';
    
    return 0;
}