import sys

sys.setrecursionlimit(10**7)
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def LI2(): return list(map(int,sys.stdin.readline().rstrip()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
def LS2(): return list(sys.stdin.readline().rstrip())


N,M,P = MI()
A = LI()

max_A = max(A)
ans = 1
X = (M+max_A)//max_A

if X == 1:
    print(ans)
    exit()

for i in range(N):
    a = A[i]
    if a % P == 0:
        while a % P == 0:
            a //= P
    A[i] = a

max_A = max(A)

if max_A == 1:
    print(-1)
    exit()

x = 1
while x < X:
    x *= max_A
    ans += 1

print(ans)