n,m,p,*a=map(int,open(0).read().split())
a.sort(reverse=True)
for i in a:
    if i%p!=0 and i!=1:
        break
if i%p==0 or i==1:
    print(-1)
    exit()
x=1
j=0
while x<=m:
    x*=i
    j+=1
print(j)