from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
input = sys.stdin.readline


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

for a in A:
    while a%P==0:
        a //= P
    B.append(a)

L = max(B)
S = max(A)
if S>M:
    print(1)
    exit()

if L==1:
    print(-1)
    exit()
now = S
cnt = 1
while now <= M:
    cnt += 1
    now *= L
print(cnt)