N, K = map(int, input().split())
A = list(map(int, input().split()))

C = [dict() for _ in range(30)]
for i in range(N):
    for j in range(30):
        key = A[i] & ~((1<<(30-j))-1)
        key |= 1<<(29-j) & A[i]
        if key in C[j]:
            C[j][key] += 1
        else:
            C[j][key] = 1

ans = 0
cnt = 0
for i in range(30):
    c = 0
    for j in range(N):
        key = (ans^A[j]) & ~((1<<(30-i))-1)
        key |= 1<<(29-i) & A[j]
        if key in C[i]:
            c += C[i][key]
        if ans == 0:
            c -= 1
    c //= 2
    if cnt+c < K:
        ans |= 1<<(29-i)
        cnt += c

print(ans)