n, m, p = map(int, input().split())
A = list(map(int, input().split()))
ma_ = max(A)
if ma_ > m:
    print(1)
    exit()
for i in range(n):
    while A[i] % p == 0:
        A[i] //= p

ma = max(A)
if ma == 1:
    print(-1)
else:
    cnt = 0
    x = 1
    while x * ma_ <= m:
        x *= ma
        cnt += 1
    print(cnt + 1)