chars = input().split(" ")

leaves = int(chars[0])
per_lost = int(chars[1])

month_list = []
for x in range(int(chars[2]), int(chars[2]) + int(chars[3])):
    month_list.append(x)

if 12 in month_list:
    month_list.remove(12)
    month_list.append(0)

counter = 0

while True:
    if leaves <= 0:
        print(counter)
        break
    else:
        counter += 1

    if (counter % 12) in month_list:
        leaves -= per_lost * 2
    else:
        leaves -= per_lost