n,m,p=map(int,input().split())
a=list(map(int,input().split()))
if any([x>m for x in a]):
  print(1)
  exit()
bd=m
mxv=0
for x in a:
  bd=min(bd,(m+1+x-1)//x)
  while x%p==0:x//=p
  mxv=max(mxv,x)
if mxv==1:
  print(-1)
  exit()
now=1
ans=0
while now<=bd:
  now*=mxv
  ans+=1
if now>m:
  print(ans)
else:
  print(ans+1)