def f(x):
    while x % P == 0:
        x //= P
    return x

N, M, P, *A = map(int, open(0).read().split())

max_A = max(A)
t = max(map(f, A))

if t in [0, 1]:
    print(-1)
    exit()

x = 1
result = 1
while x * max_A <= M:
    x *= t
    result += 1
print(result)