#include <iostream>
#include <cmath>
#include <map>
using namespace std;

int a[200010];

int main() {
    int n;
    long long k;
    cin >> n >> k;
    k--;
    int maxn = 0;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
        maxn = max(maxn, a[i]);
    }
    int ans = 0;
    for (int i = log2(maxn); i >= 0; i--) {
        map<int, int> m;
        for (int j = 1; j <= n; j++) {
            m[(a[j] >> i) << i]++;
        }
        long long cnt = 0;
        for (auto j : m) {
            int t = j.first ^ ans;
            if (j.first > t) {
                continue;
            }
            if (!ans) {
                cnt += ((long long)j.second * (j.second - 1)) >> 1;
            }
            else {
                if (m.count(t)) {
                    cnt += (long long)j.second * m[t];
                }
            }
        }
        if (cnt <= k) {
            ans |= 1 << i;
            k -= cnt;
        }
    }
    cout << ans;
    return 0;
}