import sys, time, random
from collections import deque, Counter, defaultdict
def debug(*x):print('debug:',*x, file=sys.stderr)
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
inf = 2 ** 61 - 1
mod = 998244353

def xor_str(x, y):
    return ''.join(str(int(a) ^ int(b)) for a, b in zip(x, y))
n, k = mi()
a = li()

prefix_counter = Counter()
A = []
for v in a:
    s = bin(v)[2:]
    while len(s) < 30:
        s = '0' + s
    A.append(s)
    for i in range(30):
        prefix_counter[s[:i+1]] += 1

ans = ''

for i in range(30):
    #まず0を付けると仮定
    zans = ans + '0'
    zcnt = 0
    for v in A:
        prefix_counter[v[:len(zans)]] -= 1
        tocnt = xor_str(zans, v[:len(zans)])
        zcnt += prefix_counter[tocnt]
    if zcnt >= k:
        ans += '0'
    else:
        ans += '1'
        k -= zcnt
print(int(ans, 2))