N, M, P = map(int, input().split())
A = list(map(int, input().split()))
A = set(A)

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

ok = []
ng = []
for a in A:
    if a == 1:
        continue
    if a % P == 0:
        ng.append(a)
    else:
        ok.append(a)

ans = -1

if ok:
    v = max(ok)
    ans = 0
    x = 1
    while x < M:
        x *= v
        ans += 1


if ng:
    for v in ng:
        if v >= M:
            ans = 1
            continue
        tmp = v
        while tmp % P == 0:
            tmp //= P
        if tmp == 1:
            continue
        cnt = 0
        x = 1
        while x < M:
            if x % P == 0:
                x //= P
            else:
                x *= v
            cnt += 1
        if ans == -1:
            ans = cnt
        else:
            cnt = min(cnt, ans)

print(ans)