R=range
J=lambda:map(int,input().split())
N,K=J()
A=sorted(bin(n|1<<30)[3:]for n in J())
M=N*(N-1)>>1
p=[[[0,N],[0,N]]]
a=0
def D(v):return v[1]-v[0]
for d in R(30):
	m,q=0,[[],[]]
	for v in p:
		s=[]
		for l,r in v:
			for i in R(l,r):
				if A[i][d]>'0':s+=[[[l,i],[i,r]]];break
			else:s+=[[[l,r],[r,r]]]
		m+=D(s[0][0])*D(s[1][1])+(v[0]!=v[1])*D(s[1][0])*D(s[0][1])
		for e in R(2):
			for f in R(2):
				if D(s[0][e])and D(s[1][f])and(v[0]!=v[1]or e<=f):q[e!=f]+=[[s[0][e],s[1][f]]]
	if M<K+m:a,K,M,p=a*2|1,K-M+m,m,q[1]
	else:a,M,p=a*2,M-m,q[0]
print(a)