#include <iostream>
#include <vector>
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
using namespace std;
using ll = long long;
const int log = 31;
struct BinaryTrie {
	
	vector<int> par, cnt, b0, b1;
	
	explicit BinaryTrie(void) {
		par.push_back(-1);
		b0.push_back(-1);
		b1.push_back(-1);
		cnt.push_back(0);
	}

	inline int __append(int p, int nxt_bit) {
		int idx = par.size();
		par.push_back(p);
		b0.push_back(-1);
		b1.push_back(-1);
		cnt.push_back(0);
		if(nxt_bit == 0) b0[p] = idx;
		if(nxt_bit == 1) b1[p] = idx;
		return idx;
	}

	inline int move(int p, int nxt_bit) {
		if(nxt_bit == 0) {
			if(b0[p] == -1) return __append(p, nxt_bit);
			else return b0[p];
		} else {
			if(b1[p] == -1) return __append(p, nxt_bit);
			else return b1[p];
		}
	}

	void add_value(int x) {
		int root = 0;
		cnt[root]++;
		for(int i = log; i >= 0; i--) {
			root = move(root, (x>>i)&1);
			cnt[root]++;
		}
	}
	
	inline int subtree_cnt(int r) {
		if(r == -1) return 0;
		return cnt[r];
	}

	int lower_bound(int value, int x=0) {
		int lb = 0;
		int root = 0;
		for(int i = log; i >= 0; i--) {
			int nxt_bit = (value>>i)&1;
			int flip = (x>>i)&1;
			if(nxt_bit == 1) {
				if(flip) lb += subtree_cnt(b1[root]);
				else lb += subtree_cnt(b0[root]);
			}
			root = move(root, nxt_bit^flip);
		}
		return lb;
	}
	
	int upper_bound(int value, int x=0) {
		int ub = 0;
		int root = 0;
		for(int i = log; i >= 0; i--) {
			int nxt_bit = (value>>i)&1;
			int flip = (x>>i)&1;
			if(nxt_bit) {
				if(flip) ub += subtree_cnt(b1[root]);
				else ub += subtree_cnt(b0[root]);
			}
			root = move(root, nxt_bit^flip);
		}
		ub += subtree_cnt(root);
		return ub;
	}
};

int main() {
	
	BinaryTrie bt;
	
	long long n, k;
	cin >> n >> k;
	
	vector<int> a(n);
	for(int i = 0; i < n; ++i) {
		cin >> a[i];
		bt.add_value(a[i]);
	}
		
	// Find N + 2 * K kth number
	const long long pos = n + 2 * k - 1;
	int ng = -1, ok = 1e9;
	while(ok - ng > 1) {
		int x = (ok + ng) >> 1;
		long long count = 0;
		for(int i = 0; i < n; ++i) {
			count += bt.upper_bound(x, a[i]);
		}
		if(count >= pos) ok = x;
		else ng = x;
	}
	cout << ok << endl;
}