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

def kill_by_attack(hp,attack):
    time = hp / attack
    if(hp%attack != 0):
        time += 1
    return time

def kill_by_heal(n,hp,heal):
    over_flow_hp = 2 ** n - 2 ** (n - 1) - 1
    time = (over_flow_hp-hp)/heal
    if((over_flow_hp-hp)%heal != 0):
        time += 1
    return time

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