N, X = map(int, input().split())
A = list(map(int, input().split()))
C = [0 for _ in range(N + 1)]
for a in A:
  if a <= N:
    C[a] += 1
for a in range(N + 1):
  if C[a] == 0:
    A.append(a)
    break
D = [-1 for _ in range(N + 1)]
for i in range(N + 1):
  if A[i] <= N:
    D[A[i]] = i

i = 0
R = [-1 for _ in range(N + 1)]
for a in range(N + 1):
  j = D[a]
  if j != -1:
    if R[j] >= 0:
      j = i
      while R[j] >= 0:
        j += 1
      R[j] = a
      j += 1
      i = j
    else:
      R[j] = a
  else:
    while R[i] >= 0:
      i += 1
    R[i] = a
    i += 1
if X <= N + 1:
  print(A[X - 1])
else:
  print(R[(X - 1) % (N + 1)])