# Enter your code here. Read input from STDIN. Print output to STDOUT
price,diff,minn,wallet=map(int,raw_input().split())
games=0
while wallet>0:
    if price>wallet:
        break
    wallet-=price
    if price-diff>=minn:
        price-=diff
    elif price>minn:
        price=minn
    games+=1
print games