N,K = list(map(int,input().split()))
l = list(map(int,input().split()))
for i in range(N):
    l[i]=bin(l[i])[2:]
    l[i]='0'*(30-len(l[i]))+l[i]


ls = []
br = 0
k = max(l)
a = k.find('1')
for j in range(a,30):
    for i in range(len(l)):
        if str(l[i])[j]=='1':
            ls.append(l[i])
    if len(ls)>=K:
        br+=2**(30-j-1)
    if len(ls)>K:
        l = ls[:]
    ls=[]

print(br,end='')