n,m,p = map(int,input().split())
a = list(map(int,input().split()))
ans = float("INF")
ma = max(a)
if ma > m:
    print(1)
    exit()

for i in a:
    now = i
    count = 0
    while now%p == 0:
        now //= p
        count += 1
    if now == 1:
        continue
    x = 1
    c = 0
    count += 1
    while x*ma <= m:
        x *= now
        c += count
    if x > m:
        ans = min(ans,c)
    else:
        ans = min(ans,c+1)
if ans == float("INF"):
    print(-1)
else:
    print(ans)