n = input()
hp = input()
attack = input()
heal = input()

def kill_by_attack(hp,attack):
    time = 0
    while True:
        if(hp < 0):
            return time
        hp -= attack
        time += 1

def kill_by_heal(n,hp,heal):
    time = 0
    over_flow_hp = 2 ** n - 2 ** (n - 1) - 1
    while True:
        if(hp > over_flow_hp):
            return time
        hp += heal
        time += 1

print min(kill_by_attack(hp,attack),kill_by_heal(n,hp,heal))