n, m, p = map(int, input().split())
A = list(map(int, input().split()))

if m == 1:
    print(0)
    exit()

if max(A) > m:
    print(1)
    exit()

B = []
for a in A:
    while a%p == 0:
        a //= p
    B.append(a)
B.sort(reverse=True)

if B[0] == 1:
    print(-1)
    exit()

x = 1
ans =0
while x <= m:
    ans += 1
    x *= B[0]
print(ans)