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

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

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

if ng:
    v = max(ng)
    if v >= M:
        print(1)
        exit()
    tmp = v
    while tmp % P == 0:
        tmp //= P
    if tmp == 1:
        print(-1)
        exit()
    ans = 0
    x = 1
    while x < M:
        if x % P == 0:
            x //= P
        else:
            x *= v
        ans += 1
    print(ans)
    exit()

print(-1)