def main1(n,m,p,a):
  if any([x>m for x in a]):return 1
  bd=m
  mxvary=[-1]*31
  for x in a:
    bd=min(bd,(m+1+x-1)//x)
    cnt=0
    while x%p==0:
      cnt+=1
      x//=p
    mxvary[cnt]=max(mxvary[cnt],x)
  if all([abs(x)==1 for x in mxvary]):return -1
  ans=float('inf')
  for i in range(31):
    if abs(mxvary[i])==1:continue
    mxv=mxvary[i]
    tmp=0
    now=1
    while now<=bd:
      now*=mxv
      tmp+=i+1
    if now>m:
      ans=min(ans,tmp)
    else:
      ans=min(ans,tmp+1)
  return ans

if __name__=='__main__':
  n,m,p=map(int,input().split())
  a=list(map(int,input().split()))
  ret1=main1(n,m,p,a)
  print(ret1)