n, m, p = map(int, input().split())
a = list(map(int, input().split()))
ans = 10 ** 9
s = set()
t = 1
for k in a:
    t = 1
    while k % p == 0:
        k //= p
        t += 1
    if k == 1:
        continue
    x = 1
    res = 0
    while x <= m:
        x *= k
        res += t
    ans = min(ans, res)
if ans != 10 ** 9:
    print(ans)
else:
    print(-1)