N,M,P=map(int,input().split())
A=list(map(int,input().split()))

B=[]
for a in A:
    while a%P==0:
        a//=P
    B.append(a)

S=max(B)
if S==1:
    print(-1)
    exit(0)

t=1
K=0
while t<=M:
    t*=S
    K+=1

print(K)