# Pythonは低速なので通るわけがない

class BinaryTrie:

    def __init__(self, log):
        self.lg = log
        self.b0 = [-1]
        self.b1 = [-1]
        self.cnt = [0]

    def __append(self, p, nxt_bit):
        idx = len(self.cnt)
        self.b0.append(-1)
        self.b1.append(-1)
        self.cnt.append(0)
        if nxt_bit: self.b1[p] = idx
        else: self.b0[p] = idx
        return idx

    def move(self, p, nxt_bit):
        if nxt_bit:
            if self.b1[p] == -1: return self.__append(p, nxt_bit)
            return self.b1[p]
        else:
            if self.b0[p] == -1: return self.__append(p, nxt_bit)
            return self.b0[p]
    
    def subtree_cnt(self, r):
        if r == -1: return 0
        return self.cnt[r]

    def add_value(self, x):
        r = 0
        self.cnt[r] += 1
        for i in range(self.lg, -1, -1):
            r = self.move(r, (x>>i)&1)
            self.cnt[r] += 1

    def lower_bound(self, value, x=0):
        lb = 0
        r = 0
        for i in range(self.lg, -1, -1):
            if self.cnt[r] == 0: return lb
            nxt_bit = (value>>i)&1
            flip = (x>>i)&1
            if nxt_bit:
                if flip: lb += self.subtree_cnt(self.b1[r])
                else: lb += self.subtree_cnt(self.b0[r])
            if nxt_bit^flip == 0 and self.b0[r] == -1: return lb
            if nxt_bit^flip == 1 and self.b1[r] == -1: return lb
            r = self.move(r, nxt_bit^flip)
        return lb
    
    def upper_bound(self, value, x=0):
        ub = 0
        r = 0
        for i in range(self.lg, -1, -1):
            if self.cnt[r] == 0: return ub
            nxt_bit = (value>>i)&1
            flip = (x>>i)&1
            if nxt_bit:
                if flip: ub += self.subtree_cnt(self.b1[r])
                else: ub += self.subtree_cnt(self.b0[r])
            if nxt_bit^flip == 0 and self.b0[r] == -1: return ub
            if nxt_bit^flip == 1 and self.b1[r] == -1: return ub
            r = self.move(r, nxt_bit^flip)
        ub += self.subtree_cnt(r)
        return ub

n, k = map(int, input().split())
bt = BinaryTrie(30)
a = list(map(int, input().split()))
for v in a: bt.add_value(v)

pos = n + 2 * k - 1

ng, ok = -1, (1 << 30) - 1
while ok - ng > 1:
    x = (ok + ng) >> 1
    count = 0

    for i in range(n):
        count += bt.upper_bound(x, a[i])
        if count >= pos: break
        
    if count >= pos: ok = x
    else: ng = x

print(ok)