n,m,p = map(int,input().split())
a = list(map(int,input().split()))
m_a = max(a)

s = -1
for x in a:
    if x%p == 0:
        pass
    else:
        s = max(s, x)
if s == -1:
    print(-1)
else:
    ans = 0
    x = 1
    while x <= m:
        x *= s
        ans += 1
    print(ans)