# coding:UTF-8
import sys

MOD = 10 ** 9 + 7
INF = float('inf')

N, M, P = list(map(int, input().split()))     # スペース区切り連続数字
A = list(map(int, input().split()))     # スペース区切り連続数字

if M == 1:
    print("0")
    exit()
if max(A) > M:
    print("1")
    exit()

B = [0] * N
C = [0] * N

for i in range(N):
    c = 1
    b = A[i]
    while True:
        if b % 2 == 0:
            b //= 2
            c += 1
        else:
            B[i] = b
            C[i] = c
            break

res = INF
for i in range(N):
    if B[i] == 1:
        continue

    x = M // (A[i] * B[i])
    if (A[i] * B[i]) * (x - 1) > M:
        t = C[i] * (x - 1) + 1
        res = min(res, t)
    elif (A[i] * B[i]) * x > M:
        t = C[i] * x + 1
        res = min(res, t)
    elif (A[i] * B[i]) * (x + 1) > M:
        t = C[i] * (x + 1) + 1
        res = min(res, t)

if res == INF:
    print("-1")
else:
    print(res)