n,m,p,*a=map(int,open(0).read().split())
a.sort(reverse=True)
b=[i if i%p else i//p for i in a]
b.sort(reverse=True)
x=1
j=0
while x<=m:
    if x*a[0]>m:
        print(j+1)
        exit()
    if b[0]==1:
        print(-1)
        exit()
    x*=b[0]
    j+=1