N, M, P = map(int, input().split())
A = list(map(int, input().split()))
ma = max(A)
if ma >= M:
    print(1)
    exit()
    
for i in range(N):
    while A[i] % P == 0:
        A[i] //= P
        
x = max(A)
if x == 1:
    print(-1)
    exit()
    
ans = 2
now = x
while now * ma < M:
    now *= x
    ans += 1
    
print(ans)