l = input().split()
l = list(map(int,l))
leaves = l[0]
fallen = l[1]
wind_season  = l[2]
wind_lasting = l[3]
month = 1
wind_count = 0
count = 0
is_wind = False

while True:
    if leaves <= 0:
        print(count)
        break
    if month == wind_season:
        is_wind = True
    if is_wind:
        wind_count += 1
    if wind_count > wind_lasting:
        wind_count = 0
        is_wind = False
    if is_wind:
        leaves -= (fallen * 2)
    else:
        leaves -= fallen
    count += 1
    month += 1
    if month == 13:
        month = 1