n,m,p=map(int,input().split())
a=list(map(int,input().split()))
ma0=max(a)
for i in range(n):
  if a[i]>m:
    print(1)
    exit()
  while a[i]%p==0:a[i]//=p
ma1=max(a)
if ma1==1:
  print(-1)
  exit()
now=1
ans=0
while now*ma0<=m:
  now*=ma1
  ans+=1
print(ans+1)