N,M,P = map(int, input().split())
A = list(map(int, input().split()))
divA = [0]*N
cntDiv = [0]*N
maxA = max(A)
if maxA>M:
    print(1)
    exit()
aaa=0
for i in range(N):
    cnt = 0
    temp = A[i]
    while temp % P ==0:
        temp=temp//P
        cnt+=1
    divA[i]=temp
    cntDiv[i]=cnt
    aaa=max(aaa,temp/(cnt+1))

if divA.count(1)==N:
    print(-1)
    exit()

cnt = 1
x = 1
while maxA*x<M:
    cnt+=1
    x*=aaa

print(cnt)