N, M, P = map(int, input().split())
A = list(map(int, input().split()))
maxa = max(A)
for i in range(N):
  while A[i]%P==0:
    A[i] //= P
maxa2 = max(A)
ans = 0
x = 1
if M==1:
  print(0)
else:
  while x<=M:
    ans += 1
    if x*maxa>M:
      break
    if ans>1 and maxa2==1:
      ans = -1
      break
    x *= maxa2
  print(ans)